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href='../../core/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a> </nav> <div class="theme-picker"> <button id="theme-picker" aria-label="Pick another theme!"> <img src="../../brush.svg" width="18" alt="Pick another theme!"> </button> <div id="theme-choices"></div> </div> <script src="../../theme.js"></script> <nav class="sub"> <form class="search-form js-only"> <div class="search-container"> <input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"> </div> </form> </nav> <section id='main' class="content"><pre class="line-numbers"><span id="1"> 1</span> <span id="2"> 2</span> <span id="3"> 3</span> <span id="4"> 4</span> <span id="5"> 5</span> <span id="6"> 6</span> <span id="7"> 7</span> <span id="8"> 8</span> <span id="9"> 9</span> <span id="10"> 10</span> <span id="11"> 11</span> <span id="12"> 12</span> <span id="13"> 13</span> <span 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871</span> <span id="872"> 872</span> <span id="873"> 873</span> <span id="874"> 874</span> <span id="875"> 875</span> <span id="876"> 876</span> <span id="877"> 877</span> <span id="878"> 878</span> <span id="879"> 879</span> <span id="880"> 880</span> <span id="881"> 881</span> <span id="882"> 882</span> <span id="883"> 883</span> <span id="884"> 884</span> <span id="885"> 885</span> <span id="886"> 886</span> <span id="887"> 887</span> <span id="888"> 888</span> <span id="889"> 889</span> <span id="890"> 890</span> <span id="891"> 891</span> <span id="892"> 892</span> <span id="893"> 893</span> <span id="894"> 894</span> <span id="895"> 895</span> <span id="896"> 896</span> <span id="897"> 897</span> <span id="898"> 898</span> <span id="899"> 899</span> <span id="900"> 900</span> <span id="901"> 901</span> <span id="902"> 902</span> <span id="903"> 903</span> <span id="904"> 904</span> <span id="905"> 905</span> <span id="906"> 906</span> <span id="907"> 907</span> <span id="908"> 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945</span> <span id="946"> 946</span> <span id="947"> 947</span> <span id="948"> 948</span> <span id="949"> 949</span> <span id="950"> 950</span> <span id="951"> 951</span> <span id="952"> 952</span> <span id="953"> 953</span> <span id="954"> 954</span> <span id="955"> 955</span> <span id="956"> 956</span> <span id="957"> 957</span> <span id="958"> 958</span> <span id="959"> 959</span> <span id="960"> 960</span> <span id="961"> 961</span> <span id="962"> 962</span> <span id="963"> 963</span> <span id="964"> 964</span> <span id="965"> 965</span> <span id="966"> 966</span> <span id="967"> 967</span> <span id="968"> 968</span> <span id="969"> 969</span> <span id="970"> 970</span> <span id="971"> 971</span> <span id="972"> 972</span> <span id="973"> 973</span> <span id="974"> 974</span> <span id="975"> 975</span> <span id="976"> 976</span> <span id="977"> 977</span> <span id="978"> 978</span> <span id="979"> 979</span> <span id="980"> 980</span> <span id="981"> 981</span> <span id="982"> 982</span> <span id="983"> 983</span> <span id="984"> 984</span> <span id="985"> 985</span> <span id="986"> 986</span> <span id="987"> 987</span> <span id="988"> 988</span> <span id="989"> 989</span> <span id="990"> 990</span> <span id="991"> 991</span> <span id="992"> 992</span> <span id="993"> 993</span> <span id="994"> 994</span> <span id="995"> 995</span> <span id="996"> 996</span> <span id="997"> 997</span> <span id="998"> 998</span> <span id="999"> 999</span> <span id="1000">1000</span> <span id="1001">1001</span> <span id="1002">1002</span> <span id="1003">1003</span> <span id="1004">1004</span> <span id="1005">1005</span> <span id="1006">1006</span> <span id="1007">1007</span> <span id="1008">1008</span> <span id="1009">1009</span> <span id="1010">1010</span> <span id="1011">1011</span> <span id="1012">1012</span> <span id="1013">1013</span> <span id="1014">1014</span> <span id="1015">1015</span> <span id="1016">1016</span> <span id="1017">1017</span> <span id="1018">1018</span> <span id="1019">1019</span> <span id="1020">1020</span> <span id="1021">1021</span> <span id="1022">1022</span> <span id="1023">1023</span> <span id="1024">1024</span> <span id="1025">1025</span> <span id="1026">1026</span> <span id="1027">1027</span> <span id="1028">1028</span> <span id="1029">1029</span> <span id="1030">1030</span> <span id="1031">1031</span> <span id="1032">1032</span> <span id="1033">1033</span> <span id="1034">1034</span> <span id="1035">1035</span> <span id="1036">1036</span> <span id="1037">1037</span> <span id="1038">1038</span> <span id="1039">1039</span> <span id="1040">1040</span> <span id="1041">1041</span> <span id="1042">1042</span> <span id="1043">1043</span> <span id="1044">1044</span> <span id="1045">1045</span> <span id="1046">1046</span> <span id="1047">1047</span> <span id="1048">1048</span> <span id="1049">1049</span> <span id="1050">1050</span> <span id="1051">1051</span> <span id="1052">1052</span> <span id="1053">1053</span> <span id="1054">1054</span> <span id="1055">1055</span> <span id="1056">1056</span> <span id="1057">1057</span> <span id="1058">1058</span> <span id="1059">1059</span> <span id="1060">1060</span> <span id="1061">1061</span> <span id="1062">1062</span> <span id="1063">1063</span> <span id="1064">1064</span> <span id="1065">1065</span> <span id="1066">1066</span> <span id="1067">1067</span> <span id="1068">1068</span> <span id="1069">1069</span> <span id="1070">1070</span> <span id="1071">1071</span> <span id="1072">1072</span> <span id="1073">1073</span> <span id="1074">1074</span> <span id="1075">1075</span> <span id="1076">1076</span> <span id="1077">1077</span> <span id="1078">1078</span> <span id="1079">1079</span> <span id="1080">1080</span> <span id="1081">1081</span> <span id="1082">1082</span> <span id="1083">1083</span> <span id="1084">1084</span> <span id="1085">1085</span> <span id="1086">1086</span> <span id="1087">1087</span> <span id="1088">1088</span> <span id="1089">1089</span> <span id="1090">1090</span> <span id="1091">1091</span> <span id="1092">1092</span> <span id="1093">1093</span> <span id="1094">1094</span> <span id="1095">1095</span> <span id="1096">1096</span> <span id="1097">1097</span> <span id="1098">1098</span> <span id="1099">1099</span> <span id="1100">1100</span> <span id="1101">1101</span> <span id="1102">1102</span> <span id="1103">1103</span> <span id="1104">1104</span> <span id="1105">1105</span> <span id="1106">1106</span> <span id="1107">1107</span> <span id="1108">1108</span> <span id="1109">1109</span> <span id="1110">1110</span> <span id="1111">1111</span> <span id="1112">1112</span> <span id="1113">1113</span> <span id="1114">1114</span> <span id="1115">1115</span> <span id="1116">1116</span> <span id="1117">1117</span> <span id="1118">1118</span> <span id="1119">1119</span> <span id="1120">1120</span> <span id="1121">1121</span> <span id="1122">1122</span> <span id="1123">1123</span> <span id="1124">1124</span> <span id="1125">1125</span> <span id="1126">1126</span> <span id="1127">1127</span> <span id="1128">1128</span> <span id="1129">1129</span> <span id="1130">1130</span> <span id="1131">1131</span> <span id="1132">1132</span> <span id="1133">1133</span> <span id="1134">1134</span> <span id="1135">1135</span> <span id="1136">1136</span> <span id="1137">1137</span> <span id="1138">1138</span> <span id="1139">1139</span> <span id="1140">1140</span> <span id="1141">1141</span> <span id="1142">1142</span> <span id="1143">1143</span> <span id="1144">1144</span> <span id="1145">1145</span> <span id="1146">1146</span> <span id="1147">1147</span> <span id="1148">1148</span> <span id="1149">1149</span> <span id="1150">1150</span> <span id="1151">1151</span> <span id="1152">1152</span> <span id="1153">1153</span> <span id="1154">1154</span> <span id="1155">1155</span> <span id="1156">1156</span> <span id="1157">1157</span> <span id="1158">1158</span> <span id="1159">1159</span> <span id="1160">1160</span> <span id="1161">1161</span> <span id="1162">1162</span> <span id="1163">1163</span> <span id="1164">1164</span> <span id="1165">1165</span> <span id="1166">1166</span> <span id="1167">1167</span> <span id="1168">1168</span> <span id="1169">1169</span> <span id="1170">1170</span> <span id="1171">1171</span> <span id="1172">1172</span> <span id="1173">1173</span> <span id="1174">1174</span> <span id="1175">1175</span> <span id="1176">1176</span> <span id="1177">1177</span> <span id="1178">1178</span> <span id="1179">1179</span> <span id="1180">1180</span> <span id="1181">1181</span> <span id="1182">1182</span> <span id="1183">1183</span> <span id="1184">1184</span> <span id="1185">1185</span> <span id="1186">1186</span> <span id="1187">1187</span> <span id="1188">1188</span> <span id="1189">1189</span> <span id="1190">1190</span> <span id="1191">1191</span> <span id="1192">1192</span> <span id="1193">1193</span> <span id="1194">1194</span> <span id="1195">1195</span> <span id="1196">1196</span> <span id="1197">1197</span> <span id="1198">1198</span> <span id="1199">1199</span> <span id="1200">1200</span> <span id="1201">1201</span> <span id="1202">1202</span> <span id="1203">1203</span> <span id="1204">1204</span> <span id="1205">1205</span> <span id="1206">1206</span> <span id="1207">1207</span> <span id="1208">1208</span> <span id="1209">1209</span> <span id="1210">1210</span> <span id="1211">1211</span> <span id="1212">1212</span> <span id="1213">1213</span> <span id="1214">1214</span> <span id="1215">1215</span> <span id="1216">1216</span> <span id="1217">1217</span> <span id="1218">1218</span> <span id="1219">1219</span> <span id="1220">1220</span> <span id="1221">1221</span> <span id="1222">1222</span> <span id="1223">1223</span> <span id="1224">1224</span> <span id="1225">1225</span> <span id="1226">1226</span> <span id="1227">1227</span> <span id="1228">1228</span> <span id="1229">1229</span> <span id="1230">1230</span> <span id="1231">1231</span> <span id="1232">1232</span> <span id="1233">1233</span> <span id="1234">1234</span> <span id="1235">1235</span> <span id="1236">1236</span> <span id="1237">1237</span> <span id="1238">1238</span> <span id="1239">1239</span> <span id="1240">1240</span> <span id="1241">1241</span> <span id="1242">1242</span> <span id="1243">1243</span> <span id="1244">1244</span> <span id="1245">1245</span> <span id="1246">1246</span> <span id="1247">1247</span> <span id="1248">1248</span> <span id="1249">1249</span> <span id="1250">1250</span> <span id="1251">1251</span> <span id="1252">1252</span> <span id="1253">1253</span> <span id="1254">1254</span> <span id="1255">1255</span> <span id="1256">1256</span> <span id="1257">1257</span> <span id="1258">1258</span> <span id="1259">1259</span> <span id="1260">1260</span> <span id="1261">1261</span> <span id="1262">1262</span> <span id="1263">1263</span> <span id="1264">1264</span> <span id="1265">1265</span> <span id="1266">1266</span> <span id="1267">1267</span> <span id="1268">1268</span> <span id="1269">1269</span> <span id="1270">1270</span> <span id="1271">1271</span> <span id="1272">1272</span> <span id="1273">1273</span> <span id="1274">1274</span> <span id="1275">1275</span> <span id="1276">1276</span> <span id="1277">1277</span> <span id="1278">1278</span> <span id="1279">1279</span> <span id="1280">1280</span> <span id="1281">1281</span> <span id="1282">1282</span> <span id="1283">1283</span> <span id="1284">1284</span> <span id="1285">1285</span> <span id="1286">1286</span> </pre><pre class="rust "> <span class="comment">// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT</span> <span class="comment">// file at the top-level directory of this distribution and at</span> <span class="comment">// http://rust-lang.org/COPYRIGHT.</span> <span class="comment">//</span> <span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span> <span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span> <span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span> <span class="comment">// option. This file may not be copied, modified, or distributed</span> <span class="comment">// except according to those terms.</span> <span class="doccomment">//! Shareable mutable containers.</span> <span class="doccomment">//!</span> <span class="doccomment">//! Values of the `Cell<T>` and `RefCell<T>` types may be mutated through shared references (i.e.</span> <span class="doccomment">//! the common `&T` type), whereas most Rust types can only be mutated through unique (`&mut T`)</span> <span class="doccomment">//! references. We say that `Cell<T>` and `RefCell<T>` provide 'interior mutability', in contrast</span> <span class="doccomment">//! with typical Rust types that exhibit 'inherited mutability'.</span> <span class="doccomment">//!</span> <span class="doccomment">//! Cell types come in two flavors: `Cell<T>` and `RefCell<T>`. `Cell<T>` implements interior</span> <span class="doccomment">//! mutability by moving values in and out of the `Cell<T>`. To use references instead of values,</span> <span class="doccomment">//! one must use the `RefCell<T>` type, acquiring a write lock before mutating. `Cell<T>` provides</span> <span class="doccomment">//! methods to retrieve and change the current interior value:</span> <span class="doccomment">//!</span> <span class="doccomment">//! - For types that implement `Copy`, the `get` method retrieves the current interior value.</span> <span class="doccomment">//! - For types that implement `Default`, the `take` method replaces the current interior value</span> <span class="doccomment">//! with `Default::default()` and returns the replaced value.</span> <span class="doccomment">//! - For all types, the `replace` method replaces the current interior value and returns the</span> <span class="doccomment">//! replaced value and the `into_inner` method consumes the `Cell<T>` and returns the interior</span> <span class="doccomment">//! value. Additionally, the `set` method replaces the interior value, dropping the replaced</span> <span class="doccomment">//! value.</span> <span class="doccomment">//!</span> <span class="doccomment">//! `RefCell<T>` uses Rust's lifetimes to implement 'dynamic borrowing', a process whereby one can</span> <span class="doccomment">//! claim temporary, exclusive, mutable access to the inner value. Borrows for `RefCell<T>`s are</span> <span class="doccomment">//! tracked 'at runtime', unlike Rust's native reference types which are entirely tracked</span> <span class="doccomment">//! statically, at compile time. Because `RefCell<T>` borrows are dynamic it is possible to attempt</span> <span class="doccomment">//! to borrow a value that is already mutably borrowed; when this happens it results in thread</span> <span class="doccomment">//! panic.</span> <span class="doccomment">//!</span> <span class="doccomment">//! # When to choose interior mutability</span> <span class="doccomment">//!</span> <span class="doccomment">//! The more common inherited mutability, where one must have unique access to mutate a value, is</span> <span class="doccomment">//! one of the key language elements that enables Rust to reason strongly about pointer aliasing,</span> <span class="doccomment">//! statically preventing crash bugs. Because of that, inherited mutability is preferred, and</span> <span class="doccomment">//! interior mutability is something of a last resort. Since cell types enable mutation where it</span> <span class="doccomment">//! would otherwise be disallowed though, there are occasions when interior mutability might be</span> <span class="doccomment">//! appropriate, or even *must* be used, e.g.</span> <span class="doccomment">//!</span> <span class="doccomment">//! * Introducing mutability 'inside' of something immutable</span> <span class="doccomment">//! * Implementation details of logically-immutable methods.</span> <span class="doccomment">//! * Mutating implementations of `Clone`.</span> <span class="doccomment">//!</span> <span class="doccomment">//! ## Introducing mutability 'inside' of something immutable</span> <span class="doccomment">//!</span> <span class="doccomment">//! Many shared smart pointer types, including `Rc<T>` and `Arc<T>`, provide containers that can be</span> <span class="doccomment">//! cloned and shared between multiple parties. Because the contained values may be</span> <span class="doccomment">//! multiply-aliased, they can only be borrowed with `&`, not `&mut`. Without cells it would be</span> <span class="doccomment">//! impossible to mutate data inside of these smart pointers at all.</span> <span class="doccomment">//!</span> <span class="doccomment">//! It's very common then to put a `RefCell<T>` inside shared pointer types to reintroduce</span> <span class="doccomment">//! mutability:</span> <span class="doccomment">//!</span> <span class="doccomment">//! ```</span> <span class="doccomment">//! use std::collections::HashMap;</span> <span class="doccomment">//! use std::cell::RefCell;</span> <span class="doccomment">//! use std::rc::Rc;</span> <span class="doccomment">//!</span> <span class="doccomment">//! fn main() {</span> <span class="doccomment">//! let shared_map: Rc<RefCell<_>> = Rc::new(RefCell::new(HashMap::new()));</span> <span class="doccomment">//! shared_map.borrow_mut().insert("africa", 92388);</span> <span class="doccomment">//! shared_map.borrow_mut().insert("kyoto", 11837);</span> <span class="doccomment">//! shared_map.borrow_mut().insert("piccadilly", 11826);</span> <span class="doccomment">//! shared_map.borrow_mut().insert("marbles", 38);</span> <span class="doccomment">//! }</span> <span class="doccomment">//! ```</span> <span class="doccomment">//!</span> <span class="doccomment">//! Note that this example uses `Rc<T>` and not `Arc<T>`. `RefCell<T>`s are for single-threaded</span> <span class="doccomment">//! scenarios. Consider using `RwLock<T>` or `Mutex<T>` if you need shared mutability in a</span> <span class="doccomment">//! multi-threaded situation.</span> <span class="doccomment">//!</span> <span class="doccomment">//! ## Implementation details of logically-immutable methods</span> <span class="doccomment">//!</span> <span class="doccomment">//! Occasionally it may be desirable not to expose in an API that there is mutation happening</span> <span class="doccomment">//! "under the hood". This may be because logically the operation is immutable, but e.g. caching</span> <span class="doccomment">//! forces the implementation to perform mutation; or because you must employ mutation to implement</span> <span class="doccomment">//! a trait method that was originally defined to take `&self`.</span> <span class="doccomment">//!</span> <span class="doccomment">//! ```</span> <span class="doccomment">//! # #![allow(dead_code)]</span> <span class="doccomment">//! use std::cell::RefCell;</span> <span class="doccomment">//!</span> <span class="doccomment">//! struct Graph {</span> <span class="doccomment">//! edges: Vec<(i32, i32)>,</span> <span class="doccomment">//! span_tree_cache: RefCell<Option<Vec<(i32, i32)>>></span> <span class="doccomment">//! }</span> <span class="doccomment">//!</span> <span class="doccomment">//! impl Graph {</span> <span class="doccomment">//! fn minimum_spanning_tree(&self) -> Vec<(i32, i32)> {</span> <span class="doccomment">//! // Create a new scope to contain the lifetime of the</span> <span class="doccomment">//! // dynamic borrow</span> <span class="doccomment">//! {</span> <span class="doccomment">//! // Take a reference to the inside of cache cell</span> <span class="doccomment">//! let mut cache = self.span_tree_cache.borrow_mut();</span> <span class="doccomment">//! if cache.is_some() {</span> <span class="doccomment">//! return cache.as_ref().unwrap().clone();</span> <span class="doccomment">//! }</span> <span class="doccomment">//!</span> <span class="doccomment">//! let span_tree = self.calc_span_tree();</span> <span class="doccomment">//! *cache = Some(span_tree);</span> <span class="doccomment">//! }</span> <span class="doccomment">//!</span> <span class="doccomment">//! // Recursive call to return the just-cached value.</span> <span class="doccomment">//! // Note that if we had not let the previous borrow</span> <span class="doccomment">//! // of the cache fall out of scope then the subsequent</span> <span class="doccomment">//! // recursive borrow would cause a dynamic thread panic.</span> <span class="doccomment">//! // This is the major hazard of using `RefCell`.</span> <span class="doccomment">//! self.minimum_spanning_tree()</span> <span class="doccomment">//! }</span> <span class="doccomment">//! # fn calc_span_tree(&self) -> Vec<(i32, i32)> { vec![] }</span> <span class="doccomment">//! }</span> <span class="doccomment">//! ```</span> <span class="doccomment">//!</span> <span class="doccomment">//! ## Mutating implementations of `Clone`</span> <span class="doccomment">//!</span> <span class="doccomment">//! This is simply a special - but common - case of the previous: hiding mutability for operations</span> <span class="doccomment">//! that appear to be immutable. The `clone` method is expected to not change the source value, and</span> <span class="doccomment">//! is declared to take `&self`, not `&mut self`. Therefore any mutation that happens in the</span> <span class="doccomment">//! `clone` method must use cell types. For example, `Rc<T>` maintains its reference counts within a</span> <span class="doccomment">//! `Cell<T>`.</span> <span class="doccomment">//!</span> <span class="doccomment">//! ```</span> <span class="doccomment">//! #![feature(core_intrinsics)]</span> <span class="doccomment">//! #![feature(shared)]</span> <span class="doccomment">//! use std::cell::Cell;</span> <span class="doccomment">//! use std::ptr::Shared;</span> <span class="doccomment">//! use std::intrinsics::abort;</span> <span class="doccomment">//!</span> <span class="doccomment">//! struct Rc<T: ?Sized> {</span> <span class="doccomment">//! ptr: Shared<RcBox<T>></span> <span class="doccomment">//! }</span> <span class="doccomment">//!</span> <span class="doccomment">//! struct RcBox<T: ?Sized> {</span> <span class="doccomment">//! strong: Cell<usize>,</span> <span class="doccomment">//! refcount: Cell<usize>,</span> <span class="doccomment">//! value: T,</span> <span class="doccomment">//! }</span> <span class="doccomment">//!</span> <span class="doccomment">//! impl<T: ?Sized> Clone for Rc<T> {</span> <span class="doccomment">//! fn clone(&self) -> Rc<T> {</span> <span class="doccomment">//! self.inc_strong();</span> <span class="doccomment">//! Rc { ptr: self.ptr }</span> <span class="doccomment">//! }</span> <span class="doccomment">//! }</span> <span class="doccomment">//!</span> <span class="doccomment">//! trait RcBoxPtr<T: ?Sized> {</span> <span class="doccomment">//!</span> <span class="doccomment">//! fn inner(&self) -> &RcBox<T>;</span> <span class="doccomment">//!</span> <span class="doccomment">//! fn strong(&self) -> usize {</span> <span class="doccomment">//! self.inner().strong.get()</span> <span class="doccomment">//! }</span> <span class="doccomment">//!</span> <span class="doccomment">//! fn inc_strong(&self) {</span> <span class="doccomment">//! self.inner()</span> <span class="doccomment">//! .strong</span> <span class="doccomment">//! .set(self.strong()</span> <span class="doccomment">//! .checked_add(1)</span> <span class="doccomment">//! .unwrap_or_else(|| unsafe { abort() }));</span> <span class="doccomment">//! }</span> <span class="doccomment">//! }</span> <span class="doccomment">//!</span> <span class="doccomment">//! impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {</span> <span class="doccomment">//! fn inner(&self) -> &RcBox<T> {</span> <span class="doccomment">//! unsafe {</span> <span class="doccomment">//! self.ptr.as_ref()</span> <span class="doccomment">//! }</span> <span class="doccomment">//! }</span> <span class="doccomment">//! }</span> <span class="doccomment">//! ```</span> <span class="doccomment">//!</span> <span class="attribute">#![<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">use</span> <span class="ident">cmp</span>::<span class="ident">Ordering</span>; <span class="kw">use</span> <span class="ident">fmt</span>::{<span class="self">self</span>, <span class="ident">Debug</span>, <span class="ident">Display</span>}; <span class="kw">use</span> <span class="ident">marker</span>::<span class="ident">Unsize</span>; <span class="kw">use</span> <span class="ident">mem</span>; <span class="kw">use</span> <span class="ident">ops</span>::{<span class="ident">Deref</span>, <span class="ident">DerefMut</span>, <span class="ident">CoerceUnsized</span>}; <span class="kw">use</span> <span class="ident">ptr</span>; <span class="doccomment">/// A mutable memory location.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// Here you can see how using `Cell<T>` allows to use mutable field inside</span> <span class="doccomment">/// immutable struct (which is also called 'interior mutability').</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// struct SomeStruct {</span> <span class="doccomment">/// regular_field: u8,</span> <span class="doccomment">/// special_field: Cell<u8>,</span> <span class="doccomment">/// }</span> <span class="doccomment">///</span> <span class="doccomment">/// let my_struct = SomeStruct {</span> <span class="doccomment">/// regular_field: 0,</span> <span class="doccomment">/// special_field: Cell::new(1),</span> <span class="doccomment">/// };</span> <span class="doccomment">///</span> <span class="doccomment">/// let new_value = 100;</span> <span class="doccomment">///</span> <span class="doccomment">/// // ERROR, because my_struct is immutable</span> <span class="doccomment">/// // my_struct.regular_field = new_value;</span> <span class="doccomment">///</span> <span class="doccomment">/// // WORKS, although `my_struct` is immutable, field `special_field` is mutable because it is Cell</span> <span class="doccomment">/// my_struct.special_field.set(new_value);</span> <span class="doccomment">/// assert_eq!(my_struct.special_field.get(), new_value);</span> <span class="doccomment">/// ```</span> <span class="doccomment">///</span> <span class="doccomment">/// See the [module-level documentation](index.html) for more.</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">value</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, } <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>:<span class="ident">Copy</span><span class="op">></span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Returns a copy of the contained value.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = Cell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// let five = c.get();</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">T</span> { <span class="kw">unsafe</span>{ <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() } } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Send</span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="op">!</span><span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>:<span class="ident">Copy</span><span class="op">></span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="self">self</span>.<span class="ident">get</span>()) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>:<span class="ident">Default</span><span class="op">></span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Creates a `Cell<T>`, with the `Default` value for T.</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-></span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="ident">Default</span>::<span class="ident">default</span>()) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>:<span class="ident">PartialEq</span> <span class="op">+</span> <span class="ident">Copy</span><span class="op">></span> <span class="ident">PartialEq</span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="self">self</span>.<span class="ident">get</span>() <span class="op">==</span> <span class="ident">other</span>.<span class="ident">get</span>() } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_eq"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>:<span class="ident">Eq</span> <span class="op">+</span> <span class="ident">Copy</span><span class="op">></span> <span class="ident">Eq</span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_ord"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.10.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>:<span class="ident">PartialOrd</span> <span class="op">+</span> <span class="ident">Copy</span><span class="op">></span> <span class="ident">PartialOrd</span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">partial_cmp</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Ordering</span><span class="op">></span> { <span class="self">self</span>.<span class="ident">get</span>().<span class="ident">partial_cmp</span>(<span class="kw-2">&</span><span class="ident">other</span>.<span class="ident">get</span>()) } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">lt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="self">self</span>.<span class="ident">get</span>() <span class="op"><</span> <span class="ident">other</span>.<span class="ident">get</span>() } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">le</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="self">self</span>.<span class="ident">get</span>() <span class="op"><=</span> <span class="ident">other</span>.<span class="ident">get</span>() } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">gt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="self">self</span>.<span class="ident">get</span>() <span class="op">></span> <span class="ident">other</span>.<span class="ident">get</span>() } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">ge</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="self">self</span>.<span class="ident">get</span>() <span class="op">>=</span> <span class="ident">other</span>.<span class="ident">get</span>() } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_ord"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.10.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>:<span class="ident">Ord</span> <span class="op">+</span> <span class="ident">Copy</span><span class="op">></span> <span class="ident">Ord</span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">cmp</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Ordering</span> { <span class="self">self</span>.<span class="ident">get</span>().<span class="ident">cmp</span>(<span class="kw-2">&</span><span class="ident">other</span>.<span class="ident">get</span>()) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_from"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.12.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="ident">t</span>) } } <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Creates a new `Cell` containing the given value.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = Cell::new(5);</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">const</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">value</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Cell</span> { <span class="ident">value</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">value</span>), } } <span class="doccomment">/// Returns a raw pointer to the underlying data in this cell.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = Cell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// let ptr = c.as_ptr();</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_as_ptr"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.12.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">as_ptr</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span> { <span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() } <span class="doccomment">/// Returns a mutable reference to the underlying data.</span> <span class="doccomment">///</span> <span class="doccomment">/// This call borrows `Cell` mutably (at compile-time) which guarantees</span> <span class="doccomment">/// that we possess the only reference.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let mut c = Cell::new(5);</span> <span class="doccomment">/// *c.get_mut() += 1;</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(c.get(), 6);</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_get_mut"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.11.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span> { <span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() } } <span class="doccomment">/// Sets the contained value.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = Cell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// c.set(10);</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">set</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">val</span>: <span class="ident">T</span>) { <span class="kw">let</span> <span class="ident">old</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">replace</span>(<span class="ident">val</span>); <span class="ident">drop</span>(<span class="ident">old</span>); } <span class="doccomment">/// Swaps the values of two Cells.</span> <span class="doccomment">/// Difference with `std::mem::swap` is that this function doesn't require `&mut` reference.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c1 = Cell::new(5i32);</span> <span class="doccomment">/// let c2 = Cell::new(10i32);</span> <span class="doccomment">/// c1.swap(&c2);</span> <span class="doccomment">/// assert_eq!(10, c1.get());</span> <span class="doccomment">/// assert_eq!(5, c2.get());</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"move_cell"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.17.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">swap</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="self">Self</span>) { <span class="kw">if</span> <span class="ident">ptr</span>::<span class="ident">eq</span>(<span class="self">self</span>, <span class="ident">other</span>) { <span class="kw">return</span>; } <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">swap</span>(<span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>(), <span class="ident">other</span>.<span class="ident">value</span>.<span class="ident">get</span>()); } } <span class="doccomment">/// Replaces the contained value, and returns it.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let cell = Cell::new(5);</span> <span class="doccomment">/// assert_eq!(cell.get(), 5);</span> <span class="doccomment">/// assert_eq!(cell.replace(10), 5);</span> <span class="doccomment">/// assert_eq!(cell.get(), 10);</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"move_cell"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.17.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">replace</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">val</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">T</span> { <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() }, <span class="ident">val</span>) } <span class="doccomment">/// Unwraps the value.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = Cell::new(5);</span> <span class="doccomment">/// let five = c.into_inner();</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(five, 5);</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"move_cell"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.17.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_inner</span>(<span class="self">self</span>) <span class="op">-></span> <span class="ident">T</span> { <span class="self">self</span>.<span class="ident">value</span>.<span class="ident">into_inner</span>() } } <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Default</span><span class="op">></span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Takes the value of the cell, leaving `Default::default()` in its place.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::Cell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = Cell::new(5);</span> <span class="doccomment">/// let five = c.take();</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(five, 5);</span> <span class="doccomment">/// assert_eq!(c.into_inner(), 0);</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"move_cell"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.17.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">take</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">T</span> { <span class="self">self</span>.<span class="ident">replace</span>(<span class="ident">Default</span>::<span class="ident">default</span>()) } } <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"coerce_unsized"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"27732"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">CoerceUnsized</span><span class="op"><</span><span class="ident">U</span><span class="op">></span>, <span class="ident">U</span><span class="op">></span> <span class="ident">CoerceUnsized</span><span class="op"><</span><span class="ident">Cell</span><span class="op"><</span><span class="ident">U</span><span class="op">>></span> <span class="kw">for</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="doccomment">/// A mutable memory location with dynamically checked borrow rules</span> <span class="doccomment">///</span> <span class="doccomment">/// See the [module-level documentation](index.html) for more.</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> { <span class="ident">borrow</span>: <span class="ident">Cell</span><span class="op"><</span><span class="ident">BorrowFlag</span><span class="op">></span>, <span class="ident">value</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, } <span class="doccomment">/// An error returned by [`RefCell::try_borrow`](struct.RefCell.html#method.try_borrow).</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">BorrowError</span> { <span class="ident">_private</span>: (), } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span> <span class="kw">impl</span> <span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">BorrowError</span> { <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> { <span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"BorrowError"</span>).<span class="ident">finish</span>() } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span> <span class="kw">impl</span> <span class="ident">Display</span> <span class="kw">for</span> <span class="ident">BorrowError</span> { <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> { <span class="ident">Display</span>::<span class="ident">fmt</span>(<span class="string">"already mutably borrowed"</span>, <span class="ident">f</span>) } } <span class="doccomment">/// An error returned by [`RefCell::try_borrow_mut`](struct.RefCell.html#method.try_borrow_mut).</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">BorrowMutError</span> { <span class="ident">_private</span>: (), } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span> <span class="kw">impl</span> <span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">BorrowMutError</span> { <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> { <span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"BorrowMutError"</span>).<span class="ident">finish</span>() } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span> <span class="kw">impl</span> <span class="ident">Display</span> <span class="kw">for</span> <span class="ident">BorrowMutError</span> { <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> { <span class="ident">Display</span>::<span class="ident">fmt</span>(<span class="string">"already borrowed"</span>, <span class="ident">f</span>) } } <span class="comment">// Values [1, MAX-1] represent the number of `Ref` active</span> <span class="comment">// (will not outgrow its range since `usize` is the size of the address space)</span> <span class="kw">type</span> <span class="ident">BorrowFlag</span> <span class="op">=</span> <span class="ident">usize</span>; <span class="kw">const</span> <span class="ident">UNUSED</span>: <span class="ident">BorrowFlag</span> <span class="op">=</span> <span class="number">0</span>; <span class="kw">const</span> <span class="ident">WRITING</span>: <span class="ident">BorrowFlag</span> <span class="op">=</span> <span class="op">!</span><span class="number">0</span>; <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Creates a new `RefCell` containing `value`.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">const</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">value</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">RefCell</span> { <span class="ident">value</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">value</span>), <span class="ident">borrow</span>: <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="ident">UNUSED</span>), } } <span class="doccomment">/// Consumes the `RefCell`, returning the wrapped value.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// let five = c.into_inner();</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_inner</span>(<span class="self">self</span>) <span class="op">-></span> <span class="ident">T</span> { <span class="comment">// Since this function takes `self` (the `RefCell`) by value, the</span> <span class="comment">// compiler statically verifies that it is not currently borrowed.</span> <span class="comment">// Therefore the following assertion is just a `debug_assert!`.</span> <span class="macro">debug_assert</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">borrow</span>.<span class="ident">get</span>() <span class="op">==</span> <span class="ident">UNUSED</span>); <span class="self">self</span>.<span class="ident">value</span>.<span class="ident">into_inner</span>() } <span class="doccomment">/// Replaces the wrapped value with a new one, returning the old value,</span> <span class="doccomment">/// without deinitializing either one.</span> <span class="doccomment">///</span> <span class="doccomment">/// This function corresponds to [`std::mem::replace`](../mem/fn.replace.html).</span> <span class="doccomment">///</span> <span class="doccomment">/// # Panics</span> <span class="doccomment">///</span> <span class="doccomment">/// Panics if the value is currently borrowed.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">/// let cell = RefCell::new(5);</span> <span class="doccomment">/// let old_value = cell.replace(6);</span> <span class="doccomment">/// assert_eq!(old_value, 5);</span> <span class="doccomment">/// assert_eq!(cell, RefCell::new(6));</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"refcell_replace"</span>, <span class="ident">since</span><span class="op">=</span><span class="string">"1.24.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">replace</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">T</span> { <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">borrow_mut</span>(), <span class="ident">t</span>) } <span class="doccomment">/// Replaces the wrapped value with a new one computed from `f`, returning</span> <span class="doccomment">/// the old value, without deinitializing either one.</span> <span class="doccomment">///</span> <span class="doccomment">/// This function corresponds to [`std::mem::replace`](../mem/fn.replace.html).</span> <span class="doccomment">///</span> <span class="doccomment">/// # Panics</span> <span class="doccomment">///</span> <span class="doccomment">/// Panics if the value is currently borrowed.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// #![feature(refcell_replace_swap)]</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">/// let cell = RefCell::new(5);</span> <span class="doccomment">/// let old_value = cell.replace_with(|&mut old| old + 1);</span> <span class="doccomment">/// assert_eq!(old_value, 5);</span> <span class="doccomment">/// assert_eq!(cell, RefCell::new(6));</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"refcell_replace_swap"</span>, <span class="ident">issue</span><span class="op">=</span><span class="string">"43570"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">replace_with</span><span class="op"><</span><span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span>) <span class="op">-></span> <span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">T</span> { <span class="kw">let</span> <span class="ident">mut_borrow</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">borrow_mut</span>(); <span class="kw">let</span> <span class="ident">replacement</span> <span class="op">=</span> <span class="ident">f</span>(<span class="ident">mut_borrow</span>); <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="ident">mut_borrow</span>, <span class="ident">replacement</span>) } <span class="doccomment">/// Swaps the wrapped value of `self` with the wrapped value of `other`,</span> <span class="doccomment">/// without deinitializing either one.</span> <span class="doccomment">///</span> <span class="doccomment">/// This function corresponds to [`std::mem::swap`](../mem/fn.swap.html).</span> <span class="doccomment">///</span> <span class="doccomment">/// # Panics</span> <span class="doccomment">///</span> <span class="doccomment">/// Panics if the value in either `RefCell` is currently borrowed.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">/// let d = RefCell::new(6);</span> <span class="doccomment">/// c.swap(&d);</span> <span class="doccomment">/// assert_eq!(c, RefCell::new(6));</span> <span class="doccomment">/// assert_eq!(d, RefCell::new(5));</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"refcell_swap"</span>, <span class="ident">since</span><span class="op">=</span><span class="string">"1.24.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">swap</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="self">Self</span>) { <span class="ident">mem</span>::<span class="ident">swap</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">borrow_mut</span>(), <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">other</span>.<span class="ident">borrow_mut</span>()) } } <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Immutably borrows the wrapped value.</span> <span class="doccomment">///</span> <span class="doccomment">/// The borrow lasts until the returned `Ref` exits scope. Multiple</span> <span class="doccomment">/// immutable borrows can be taken out at the same time.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Panics</span> <span class="doccomment">///</span> <span class="doccomment">/// Panics if the value is currently mutably borrowed. For a non-panicking variant, use</span> <span class="doccomment">/// [`try_borrow`](#method.try_borrow).</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// let borrowed_five = c.borrow();</span> <span class="doccomment">/// let borrowed_five2 = c.borrow();</span> <span class="doccomment">/// ```</span> <span class="doccomment">///</span> <span class="doccomment">/// An example of panic:</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">/// use std::thread;</span> <span class="doccomment">///</span> <span class="doccomment">/// let result = thread::spawn(move || {</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">/// let m = c.borrow_mut();</span> <span class="doccomment">///</span> <span class="doccomment">/// let b = c.borrow(); // this causes a panic</span> <span class="doccomment">/// }).join();</span> <span class="doccomment">///</span> <span class="doccomment">/// assert!(result.is_err());</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">borrow</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Ref</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="self">self</span>.<span class="ident">try_borrow</span>().<span class="ident">expect</span>(<span class="string">"already mutably borrowed"</span>) } <span class="doccomment">/// Immutably borrows the wrapped value, returning an error if the value is currently mutably</span> <span class="doccomment">/// borrowed.</span> <span class="doccomment">///</span> <span class="doccomment">/// The borrow lasts until the returned `Ref` exits scope. Multiple immutable borrows can be</span> <span class="doccomment">/// taken out at the same time.</span> <span class="doccomment">///</span> <span class="doccomment">/// This is the non-panicking variant of [`borrow`](#method.borrow).</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// {</span> <span class="doccomment">/// let m = c.borrow_mut();</span> <span class="doccomment">/// assert!(c.try_borrow().is_err());</span> <span class="doccomment">/// }</span> <span class="doccomment">///</span> <span class="doccomment">/// {</span> <span class="doccomment">/// let m = c.borrow();</span> <span class="doccomment">/// assert!(c.try_borrow().is_ok());</span> <span class="doccomment">/// }</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">try_borrow</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">Ref</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">BorrowError</span><span class="op">></span> { <span class="kw">match</span> <span class="ident">BorrowRef</span>::<span class="ident">new</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">borrow</span>) { <span class="prelude-val">Some</span>(<span class="ident">b</span>) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">Ref</span> { <span class="ident">value</span>: <span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() }, <span class="ident">borrow</span>: <span class="ident">b</span>, }), <span class="prelude-val">None</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">BorrowError</span> { <span class="ident">_private</span>: () }), } } <span class="doccomment">/// Mutably borrows the wrapped value.</span> <span class="doccomment">///</span> <span class="doccomment">/// The borrow lasts until the returned `RefMut` exits scope. The value</span> <span class="doccomment">/// cannot be borrowed while this borrow is active.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Panics</span> <span class="doccomment">///</span> <span class="doccomment">/// Panics if the value is currently borrowed. For a non-panicking variant, use</span> <span class="doccomment">/// [`try_borrow_mut`](#method.try_borrow_mut).</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// *c.borrow_mut() = 7;</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(*c.borrow(), 7);</span> <span class="doccomment">/// ```</span> <span class="doccomment">///</span> <span class="doccomment">/// An example of panic:</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">/// use std::thread;</span> <span class="doccomment">///</span> <span class="doccomment">/// let result = thread::spawn(move || {</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">/// let m = c.borrow();</span> <span class="doccomment">///</span> <span class="doccomment">/// let b = c.borrow_mut(); // this causes a panic</span> <span class="doccomment">/// }).join();</span> <span class="doccomment">///</span> <span class="doccomment">/// assert!(result.is_err());</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">borrow_mut</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">RefMut</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="self">self</span>.<span class="ident">try_borrow_mut</span>().<span class="ident">expect</span>(<span class="string">"already borrowed"</span>) } <span class="doccomment">/// Mutably borrows the wrapped value, returning an error if the value is currently borrowed.</span> <span class="doccomment">///</span> <span class="doccomment">/// The borrow lasts until the returned `RefMut` exits scope. The value cannot be borrowed</span> <span class="doccomment">/// while this borrow is active.</span> <span class="doccomment">///</span> <span class="doccomment">/// This is the non-panicking variant of [`borrow_mut`](#method.borrow_mut).</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// {</span> <span class="doccomment">/// let m = c.borrow();</span> <span class="doccomment">/// assert!(c.try_borrow_mut().is_err());</span> <span class="doccomment">/// }</span> <span class="doccomment">///</span> <span class="doccomment">/// assert!(c.try_borrow_mut().is_ok());</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">try_borrow_mut</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">RefMut</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">BorrowMutError</span><span class="op">></span> { <span class="kw">match</span> <span class="ident">BorrowRefMut</span>::<span class="ident">new</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">borrow</span>) { <span class="prelude-val">Some</span>(<span class="ident">b</span>) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">RefMut</span> { <span class="ident">value</span>: <span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() }, <span class="ident">borrow</span>: <span class="ident">b</span>, }), <span class="prelude-val">None</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">BorrowMutError</span> { <span class="ident">_private</span>: () }), } } <span class="doccomment">/// Returns a raw pointer to the underlying data in this cell.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// let ptr = c.as_ptr();</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_as_ptr"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.12.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">as_ptr</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span> { <span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() } <span class="doccomment">/// Returns a mutable reference to the underlying data.</span> <span class="doccomment">///</span> <span class="doccomment">/// This call borrows `RefCell` mutably (at compile-time) so there is no</span> <span class="doccomment">/// need for dynamic checks.</span> <span class="doccomment">///</span> <span class="doccomment">/// However be cautious: this method expects `self` to be mutable, which is</span> <span class="doccomment">/// generally not the case when using a `RefCell`. Take a look at the</span> <span class="doccomment">/// [`borrow_mut`] method instead if `self` isn't mutable.</span> <span class="doccomment">///</span> <span class="doccomment">/// Also, please be aware that this method is only for special circumstances and is usually</span> <span class="doccomment">/// not what you want. In case of doubt, use [`borrow_mut`] instead.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`borrow_mut`]: #method.borrow_mut</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::RefCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let mut c = RefCell::new(5);</span> <span class="doccomment">/// *c.get_mut() += 1;</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(c, RefCell::new(6));</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_get_mut"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.11.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span> { <span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() } } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Send</span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="op">!</span><span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Clone</span><span class="op">></span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">RefCell</span>::<span class="ident">new</span>(<span class="self">self</span>.<span class="ident">borrow</span>().<span class="ident">clone</span>()) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>:<span class="ident">Default</span><span class="op">></span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Creates a `RefCell<T>`, with the `Default` value for T.</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-></span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">RefCell</span>::<span class="ident">new</span>(<span class="ident">Default</span>::<span class="ident">default</span>()) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">PartialEq</span><span class="op">></span> <span class="ident">PartialEq</span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">borrow</span>() <span class="op">==</span> <span class="kw-2">*</span><span class="ident">other</span>.<span class="ident">borrow</span>() } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_eq"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Eq</span><span class="op">></span> <span class="ident">Eq</span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_ord"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.10.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">PartialOrd</span><span class="op">></span> <span class="ident">PartialOrd</span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">partial_cmp</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Ordering</span><span class="op">></span> { <span class="self">self</span>.<span class="ident">borrow</span>().<span class="ident">partial_cmp</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">other</span>.<span class="ident">borrow</span>()) } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">lt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">borrow</span>() <span class="op"><</span> <span class="kw-2">*</span><span class="ident">other</span>.<span class="ident">borrow</span>() } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">le</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">borrow</span>() <span class="op"><=</span> <span class="kw-2">*</span><span class="ident">other</span>.<span class="ident">borrow</span>() } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">gt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">borrow</span>() <span class="op">></span> <span class="kw-2">*</span><span class="ident">other</span>.<span class="ident">borrow</span>() } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">ge</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">borrow</span>() <span class="op">>=</span> <span class="kw-2">*</span><span class="ident">other</span>.<span class="ident">borrow</span>() } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_ord"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.10.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Ord</span><span class="op">></span> <span class="ident">Ord</span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">cmp</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Ordering</span> { <span class="self">self</span>.<span class="ident">borrow</span>().<span class="ident">cmp</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">other</span>.<span class="ident">borrow</span>()) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_from"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.12.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">RefCell</span>::<span class="ident">new</span>(<span class="ident">t</span>) } } <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"coerce_unsized"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"27732"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">CoerceUnsized</span><span class="op"><</span><span class="ident">U</span><span class="op">></span>, <span class="ident">U</span><span class="op">></span> <span class="ident">CoerceUnsized</span><span class="op"><</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">U</span><span class="op">>></span> <span class="kw">for</span> <span class="ident">RefCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="kw">struct</span> <span class="ident">BorrowRef</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> { <span class="ident">borrow</span>: <span class="kw-2">&</span><span class="lifetime">'b</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">BorrowFlag</span><span class="op">></span>, } <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> <span class="ident">BorrowRef</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">borrow</span>: <span class="kw-2">&</span><span class="lifetime">'b</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">BorrowFlag</span><span class="op">></span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">BorrowRef</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">>></span> { <span class="kw">match</span> <span class="ident">borrow</span>.<span class="ident">get</span>() { <span class="ident">WRITING</span> <span class="op">=></span> <span class="prelude-val">None</span>, <span class="ident">b</span> <span class="op">=></span> { <span class="ident">borrow</span>.<span class="ident">set</span>(<span class="ident">b</span> <span class="op">+</span> <span class="number">1</span>); <span class="prelude-val">Some</span>(<span class="ident">BorrowRef</span> { <span class="ident">borrow</span>: <span class="ident">borrow</span> }) }, } } } <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">BorrowRef</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) { <span class="kw">let</span> <span class="ident">borrow</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">borrow</span>.<span class="ident">get</span>(); <span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">borrow</span> <span class="op">!=</span> <span class="ident">WRITING</span> <span class="op">&&</span> <span class="ident">borrow</span> <span class="op">!=</span> <span class="ident">UNUSED</span>); <span class="self">self</span>.<span class="ident">borrow</span>.<span class="ident">set</span>(<span class="ident">borrow</span> <span class="op">-</span> <span class="number">1</span>); } } <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">BorrowRef</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">BorrowRef</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> { <span class="comment">// Since this Ref exists, we know the borrow flag</span> <span class="comment">// is not set to WRITING.</span> <span class="kw">let</span> <span class="ident">borrow</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">borrow</span>.<span class="ident">get</span>(); <span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">borrow</span> <span class="op">!=</span> <span class="ident">UNUSED</span>); <span class="comment">// Prevent the borrow counter from overflowing.</span> <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">borrow</span> <span class="op">!=</span> <span class="ident">WRITING</span>); <span class="self">self</span>.<span class="ident">borrow</span>.<span class="ident">set</span>(<span class="ident">borrow</span> <span class="op">+</span> <span class="number">1</span>); <span class="ident">BorrowRef</span> { <span class="ident">borrow</span>: <span class="self">self</span>.<span class="ident">borrow</span> } } } <span class="doccomment">/// Wraps a borrowed reference to a value in a `RefCell` box.</span> <span class="doccomment">/// A wrapper type for an immutably borrowed value from a `RefCell<T>`.</span> <span class="doccomment">///</span> <span class="doccomment">/// See the [module-level documentation](index.html) for more.</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="lifetime">'b</span><span class="op">></span> { <span class="ident">value</span>: <span class="kw-2">&</span><span class="lifetime">'b</span> <span class="ident">T</span>, <span class="ident">borrow</span>: <span class="ident">BorrowRef</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span>, } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span> { <span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">T</span>; <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">T</span> { <span class="self">self</span>.<span class="ident">value</span> } } <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Copies a `Ref`.</span> <span class="doccomment">///</span> <span class="doccomment">/// The `RefCell` is already immutably borrowed, so this cannot fail.</span> <span class="doccomment">///</span> <span class="doccomment">/// This is an associated function that needs to be used as</span> <span class="doccomment">/// `Ref::clone(...)`. A `Clone` implementation or a method would interfere</span> <span class="doccomment">/// with the widespread use of `r.borrow().clone()` to clone the contents of</span> <span class="doccomment">/// a `RefCell`.</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_extras"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.15.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">clone</span>(<span class="ident">orig</span>: <span class="kw-2">&</span><span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span> { <span class="ident">Ref</span> { <span class="ident">value</span>: <span class="ident">orig</span>.<span class="ident">value</span>, <span class="ident">borrow</span>: <span class="ident">orig</span>.<span class="ident">borrow</span>.<span class="ident">clone</span>(), } } <span class="doccomment">/// Make a new `Ref` for a component of the borrowed data.</span> <span class="doccomment">///</span> <span class="doccomment">/// The `RefCell` is already immutably borrowed, so this cannot fail.</span> <span class="doccomment">///</span> <span class="doccomment">/// This is an associated function that needs to be used as `Ref::map(...)`.</span> <span class="doccomment">/// A method would interfere with methods of the same name on the contents</span> <span class="doccomment">/// of a `RefCell` used through `Deref`.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::{RefCell, Ref};</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new((5, 'b'));</span> <span class="doccomment">/// let b1: Ref<(u32, char)> = c.borrow();</span> <span class="doccomment">/// let b2: Ref<u32> = Ref::map(b1, |t| &t.0);</span> <span class="doccomment">/// assert_eq!(*b2, 5)</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_map"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.8.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">map</span><span class="op"><</span><span class="ident">U</span>: <span class="question-mark">?</span><span class="ident">Sized</span>, <span class="ident">F</span><span class="op">></span>(<span class="ident">orig</span>: <span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">U</span><span class="op">></span> <span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="ident">T</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">U</span> { <span class="ident">Ref</span> { <span class="ident">value</span>: <span class="ident">f</span>(<span class="ident">orig</span>.<span class="ident">value</span>), <span class="ident">borrow</span>: <span class="ident">orig</span>.<span class="ident">borrow</span>, } } } <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"coerce_unsized"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"27732"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Unsize</span><span class="op"><</span><span class="ident">U</span><span class="op">></span>, <span class="ident">U</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">CoerceUnsized</span><span class="op"><</span><span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">U</span><span class="op">>></span> <span class="kw">for</span> <span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std_guard_impls"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.20.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Display</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">Ref</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> { <span class="self">self</span>.<span class="ident">value</span>.<span class="ident">fmt</span>(<span class="ident">f</span>) } } <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Make a new `RefMut` for a component of the borrowed data, e.g. an enum</span> <span class="doccomment">/// variant.</span> <span class="doccomment">///</span> <span class="doccomment">/// The `RefCell` is already mutably borrowed, so this cannot fail.</span> <span class="doccomment">///</span> <span class="doccomment">/// This is an associated function that needs to be used as</span> <span class="doccomment">/// `RefMut::map(...)`. A method would interfere with methods of the same</span> <span class="doccomment">/// name on the contents of a `RefCell` used through `Deref`.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::{RefCell, RefMut};</span> <span class="doccomment">///</span> <span class="doccomment">/// let c = RefCell::new((5, 'b'));</span> <span class="doccomment">/// {</span> <span class="doccomment">/// let b1: RefMut<(u32, char)> = c.borrow_mut();</span> <span class="doccomment">/// let mut b2: RefMut<u32> = RefMut::map(b1, |t| &mut t.0);</span> <span class="doccomment">/// assert_eq!(*b2, 5);</span> <span class="doccomment">/// *b2 = 42;</span> <span class="doccomment">/// }</span> <span class="doccomment">/// assert_eq!(*c.borrow(), (42, 'b'));</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_map"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.8.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">map</span><span class="op"><</span><span class="ident">U</span>: <span class="question-mark">?</span><span class="ident">Sized</span>, <span class="ident">F</span><span class="op">></span>(<span class="ident">orig</span>: <span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">U</span><span class="op">></span> <span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">U</span> { <span class="comment">// FIXME(nll-rfc#40): fix borrow-check</span> <span class="kw">let</span> <span class="ident">RefMut</span> { <span class="ident">value</span>, <span class="ident">borrow</span> } <span class="op">=</span> <span class="ident">orig</span>; <span class="ident">RefMut</span> { <span class="ident">value</span>: <span class="ident">f</span>(<span class="ident">value</span>), <span class="ident">borrow</span>: <span class="ident">borrow</span>, } } } <span class="kw">struct</span> <span class="ident">BorrowRefMut</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> { <span class="ident">borrow</span>: <span class="kw-2">&</span><span class="lifetime">'b</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">BorrowFlag</span><span class="op">></span>, } <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">BorrowRefMut</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) { <span class="kw">let</span> <span class="ident">borrow</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">borrow</span>.<span class="ident">get</span>(); <span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">borrow</span> <span class="op">==</span> <span class="ident">WRITING</span>); <span class="self">self</span>.<span class="ident">borrow</span>.<span class="ident">set</span>(<span class="ident">UNUSED</span>); } } <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> <span class="ident">BorrowRefMut</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">borrow</span>: <span class="kw-2">&</span><span class="lifetime">'b</span> <span class="ident">Cell</span><span class="op"><</span><span class="ident">BorrowFlag</span><span class="op">></span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">BorrowRefMut</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">>></span> { <span class="kw">match</span> <span class="ident">borrow</span>.<span class="ident">get</span>() { <span class="ident">UNUSED</span> <span class="op">=></span> { <span class="ident">borrow</span>.<span class="ident">set</span>(<span class="ident">WRITING</span>); <span class="prelude-val">Some</span>(<span class="ident">BorrowRefMut</span> { <span class="ident">borrow</span>: <span class="ident">borrow</span> }) }, _ <span class="op">=></span> <span class="prelude-val">None</span>, } } } <span class="doccomment">/// A wrapper type for a mutably borrowed value from a `RefCell<T>`.</span> <span class="doccomment">///</span> <span class="doccomment">/// See the [module-level documentation](index.html) for more.</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="lifetime">'b</span><span class="op">></span> { <span class="ident">value</span>: <span class="kw-2">&</span><span class="lifetime">'b</span> <span class="kw-2">mut</span> <span class="ident">T</span>, <span class="ident">borrow</span>: <span class="ident">BorrowRefMut</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span>, } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span> { <span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">T</span>; <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">T</span> { <span class="self">self</span>.<span class="ident">value</span> } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span> { <span class="self">self</span>.<span class="ident">value</span> } } <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"coerce_unsized"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"27732"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Unsize</span><span class="op"><</span><span class="ident">U</span><span class="op">></span>, <span class="ident">U</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">CoerceUnsized</span><span class="op"><</span><span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">U</span><span class="op">>></span> <span class="kw">for</span> <span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std_guard_impls"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.20.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Display</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">RefMut</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> { <span class="self">self</span>.<span class="ident">value</span>.<span class="ident">fmt</span>(<span class="ident">f</span>) } } <span class="doccomment">/// The core primitive for interior mutability in Rust.</span> <span class="doccomment">///</span> <span class="doccomment">/// `UnsafeCell<T>` is a type that wraps some `T` and indicates unsafe interior operations on the</span> <span class="doccomment">/// wrapped type. Types with an `UnsafeCell<T>` field are considered to have an 'unsafe interior'.</span> <span class="doccomment">/// The `UnsafeCell<T>` type is the only legal way to obtain aliasable data that is considered</span> <span class="doccomment">/// mutable. In general, transmuting an `&T` type into an `&mut T` is considered undefined behavior.</span> <span class="doccomment">///</span> <span class="doccomment">/// The compiler makes optimizations based on the knowledge that `&T` is not mutably aliased or</span> <span class="doccomment">/// mutated, and that `&mut T` is unique. When building abstractions like `Cell`, `RefCell`,</span> <span class="doccomment">/// `Mutex`, etc, you need to turn these optimizations off. `UnsafeCell` is the only legal way</span> <span class="doccomment">/// to do this. When `UnsafeCell<T>` is immutably aliased, it is still safe to obtain a mutable</span> <span class="doccomment">/// reference to its interior and/or to mutate it. However, it is up to the abstraction designer</span> <span class="doccomment">/// to ensure that no two mutable references obtained this way are active at the same time, and</span> <span class="doccomment">/// that there are no active mutable references or mutations when an immutable reference is obtained</span> <span class="doccomment">/// from the cell. This is often done via runtime checks.</span> <span class="doccomment">///</span> <span class="doccomment">/// Note that while mutating or mutably aliasing the contents of an `& UnsafeCell<T>` is</span> <span class="doccomment">/// okay (provided you enforce the invariants some other way); it is still undefined behavior</span> <span class="doccomment">/// to have multiple `&mut UnsafeCell<T>` aliases.</span> <span class="doccomment">///</span> <span class="doccomment">///</span> <span class="doccomment">/// Types like `Cell<T>` and `RefCell<T>` use this type to wrap their internal data.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::UnsafeCell;</span> <span class="doccomment">/// use std::marker::Sync;</span> <span class="doccomment">///</span> <span class="doccomment">/// # #[allow(dead_code)]</span> <span class="doccomment">/// struct NotThreadSafe<T> {</span> <span class="doccomment">/// value: UnsafeCell<T>,</span> <span class="doccomment">/// }</span> <span class="doccomment">///</span> <span class="doccomment">/// unsafe impl<T> Sync for NotThreadSafe<T> {}</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">lang</span> <span class="op">=</span> <span class="string">"unsafe_cell"</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> { <span class="ident">value</span>: <span class="ident">T</span>, } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="op">!</span><span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Constructs a new instance of `UnsafeCell` which will wrap the specified</span> <span class="doccomment">/// value.</span> <span class="doccomment">///</span> <span class="doccomment">/// All access to the inner value through methods is `unsafe`.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::UnsafeCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let uc = UnsafeCell::new(5);</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">pub</span> <span class="kw">const</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">value</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">UnsafeCell</span> { <span class="ident">value</span>: <span class="ident">value</span> } } <span class="doccomment">/// Unwraps the value.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::UnsafeCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let uc = UnsafeCell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// let five = uc.into_inner();</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_inner</span>(<span class="self">self</span>) <span class="op">-></span> <span class="ident">T</span> { <span class="self">self</span>.<span class="ident">value</span> } } <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Gets a mutable pointer to the wrapped value.</span> <span class="doccomment">///</span> <span class="doccomment">/// This can be cast to a pointer of any kind.</span> <span class="doccomment">/// Ensure that the access is unique when casting to</span> <span class="doccomment">/// `&mut T`, and ensure that there are no mutations or mutable</span> <span class="doccomment">/// aliases going on when casting to `&T`</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::cell::UnsafeCell;</span> <span class="doccomment">///</span> <span class="doccomment">/// let uc = UnsafeCell::new(5);</span> <span class="doccomment">///</span> <span class="doccomment">/// let five = uc.get();</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span> { <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">value</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span> } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"unsafe_cell_default"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.10.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Default</span><span class="op">></span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="doccomment">/// Creates an `UnsafeCell`, with the `Default` value for T.</span> <span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-></span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">Default</span>::<span class="ident">default</span>()) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cell_from"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.12.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">t</span>) } } <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"coerce_unsized"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"27732"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">CoerceUnsized</span><span class="op"><</span><span class="ident">U</span><span class="op">></span>, <span class="ident">U</span><span class="op">></span> <span class="ident">CoerceUnsized</span><span class="op"><</span><span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">U</span><span class="op">>></span> <span class="kw">for</span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">allow</span>(<span class="ident">unused</span>)]</span> <span class="kw">fn</span> <span class="ident">assert_coerce_unsized</span>(<span class="ident">a</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">i32</span><span class="op">></span>, <span class="ident">b</span>: <span class="ident">Cell</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">i32</span><span class="op">></span>, <span class="ident">c</span>: <span class="ident">RefCell</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">i32</span><span class="op">></span>) { <span class="kw">let</span> _: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Send</span><span class="op">></span> <span class="op">=</span> <span class="ident">a</span>; <span class="kw">let</span> _: <span class="ident">Cell</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Send</span><span class="op">></span> <span class="op">=</span> <span class="ident">b</span>; <span class="kw">let</span> _: <span class="ident">RefCell</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Send</span><span class="op">></span> <span class="op">=</span> <span class="ident">c</span>; } </pre> </section> <section id='search' class="content hidden"></section> <section class="footer"></section> 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