<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source to the Rust file `libstd/primitive_docs.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>primitive_docs.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc source"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../std/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"><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1"> 1</span>
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</pre><pre class="rust ">
<span class="comment">// Copyright 2015 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="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"bool"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"true"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"false"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The boolean type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `bool` represents a value, which could only be either `true` or `false`. If you cast</span>
<span class="doccomment">/// a `bool` into an integer, `true` will be 1 and `false` will be 0.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Basic usage</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `bool` implements various traits, such as [`BitAnd`], [`BitOr`], [`Not`], etc.,</span>
<span class="doccomment">/// which allow us to perform boolean operations using `&`, `|` and `!`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`if`] always demands a `bool` value. [`assert!`], being an important macro in testing,</span>
<span class="doccomment">/// checks whether an expression returns `true`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let bool_val = true & false | false;</span>
<span class="doccomment">/// assert!(!bool_val);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`assert!`]: macro.assert.html</span>
<span class="doccomment">/// [`if`]: ../book/first-edition/if.html</span>
<span class="doccomment">/// [`BitAnd`]: ops/trait.BitAnd.html</span>
<span class="doccomment">/// [`BitOr`]: ops/trait.BitOr.html</span>
<span class="doccomment">/// [`Not`]: ops/trait.Not.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A trivial example of the usage of `bool`,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let praise_the_borrow_checker = true;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // using the `if` conditional</span>
<span class="doccomment">/// if praise_the_borrow_checker {</span>
<span class="doccomment">/// println!("oh, yeah!");</span>
<span class="doccomment">/// } else {</span>
<span class="doccomment">/// println!("what?!!");</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // ... or, a match pattern</span>
<span class="doccomment">/// match praise_the_borrow_checker {</span>
<span class="doccomment">/// true => println!("keep praising!"),</span>
<span class="doccomment">/// false => println!("you should praise!"),</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Also, since `bool` implements the [`Copy`](marker/trait.Copy.html) trait, we don't</span>
<span class="doccomment">/// have to worry about the move semantics (just like the integer and float primitives).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Now an example of `bool` cast to integer type:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// assert_eq!(true as i32, 1);</span>
<span class="doccomment">/// assert_eq!(false as i32, 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">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">mod</span> <span class="ident">prim_bool</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"never"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"!"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The `!` type, also called "never".</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `!` represents the type of computations which never resolve to any value at all. For example,</span>
<span class="doccomment">/// the [`exit`] function `fn exit(code: i32) -> !` exits the process without ever returning, and</span>
<span class="doccomment">/// so returns `!`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `break`, `continue` and `return` expressions also have type `!`. For example we are allowed to</span>
<span class="doccomment">/// write:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// #![feature(never_type)]</span>
<span class="doccomment">/// # fn foo() -> u32 {</span>
<span class="doccomment">/// let x: ! = {</span>
<span class="doccomment">/// return 123</span>
<span class="doccomment">/// };</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Although the `let` is pointless here, it illustrates the meaning of `!`. Since `x` is never</span>
<span class="doccomment">/// assigned a value (because `return` returns from the entire function), `x` can be given type</span>
<span class="doccomment">/// `!`. We could also replace `return 123` with a `panic!` or a never-ending `loop` and this code</span>
<span class="doccomment">/// would still be valid.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A more realistic usage of `!` is in this code:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # fn get_a_number() -> Option<u32> { None }</span>
<span class="doccomment">/// # loop {</span>
<span class="doccomment">/// let num: u32 = match get_a_number() {</span>
<span class="doccomment">/// Some(num) => num,</span>
<span class="doccomment">/// None => break,</span>
<span class="doccomment">/// };</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Both match arms must produce values of type [`u32`], but since `break` never produces a value</span>
<span class="doccomment">/// at all we know it can never produce a value which isn't a [`u32`]. This illustrates another</span>
<span class="doccomment">/// behaviour of the `!` type - expressions with type `!` will coerce into any other type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`u32`]: primitive.str.html</span>
<span class="doccomment">/// [`exit`]: process/fn.exit.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # `!` and generics</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ## Infallible errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The main place you'll see `!` used explicitly is in generic code. Consider the [`FromStr`]</span>
<span class="doccomment">/// trait:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// trait FromStr: Sized {</span>
<span class="doccomment">/// type Err;</span>
<span class="doccomment">/// fn from_str(s: &str) -> Result<Self, Self::Err>;</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When implementing this trait for [`String`] we need to pick a type for [`Err`]. And since</span>
<span class="doccomment">/// converting a string into a string will never result in an error, the appropriate type is `!`.</span>
<span class="doccomment">/// (Currently the type actually used is an enum with no variants, though this is only because `!`</span>
<span class="doccomment">/// was added to Rust at a later date and it may change in the future). With an [`Err`] type of</span>
<span class="doccomment">/// `!`, if we have to call [`String::from_str`] for some reason the result will be a</span>
<span class="doccomment">/// [`Result<String, !>`] which we can unpack like this:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```ignore (string-from-str-error-type-is-not-never-yet)</span>
<span class="doccomment">/// #[feature(exhaustive_patterns)]</span>
<span class="doccomment">/// // NOTE: This does not work today!</span>
<span class="doccomment">/// let Ok(s) = String::from_str("hello");</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Since the [`Err`] variant contains a `!`, it can never occur. If the `exhaustive_patterns`</span>
<span class="doccomment">/// feature is present this means we can exhaustively match on [`Result<T, !>`] by just taking the</span>
<span class="doccomment">/// [`Ok`] variant. This illustrates another behaviour of `!` - it can be used to "delete" certain</span>
<span class="doccomment">/// enum variants from generic types like `Result`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ## Infinite loops</span>
<span class="doccomment">///</span>
<span class="doccomment">/// While [`Result<T, !>`] is very useful for removing errors, `!` can also be used to remove</span>
<span class="doccomment">/// successes as well. If we think of [`Result<T, !>`] as "if this function returns, it has not</span>
<span class="doccomment">/// errored," we get a very intuitive idea of [`Result<!, E>`] as well: if the function returns, it</span>
<span class="doccomment">/// *has* errored.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For example, consider the case of a simple web server, which can be simplified to:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```ignore (hypothetical-example)</span>
<span class="doccomment">/// loop {</span>
<span class="doccomment">/// let (client, request) = get_request().expect("disconnected");</span>
<span class="doccomment">/// let response = request.process();</span>
<span class="doccomment">/// response.send(client);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Currently, this isn't ideal, because we simply panic whenever we fail to get a new connection.</span>
<span class="doccomment">/// Instead, we'd like to keep track of this error, like this:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```ignore (hypothetical-example)</span>
<span class="doccomment">/// loop {</span>
<span class="doccomment">/// match get_request() {</span>
<span class="doccomment">/// Err(err) => break err,</span>
<span class="doccomment">/// Ok((client, request)) => {</span>
<span class="doccomment">/// let response = request.process();</span>
<span class="doccomment">/// response.send(client);</span>
<span class="doccomment">/// },</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Now, when the server disconnects, we exit the loop with an error instead of panicking. While it</span>
<span class="doccomment">/// might be intuitive to simply return the error, we might want to wrap it in a [`Result<!, E>`]</span>
<span class="doccomment">/// instead:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```ignore (hypothetical-example)</span>
<span class="doccomment">/// fn server_loop() -> Result<!, ConnectionError> {</span>
<span class="doccomment">/// loop {</span>
<span class="doccomment">/// let (client, request) = get_request()?;</span>
<span class="doccomment">/// let response = request.process();</span>
<span class="doccomment">/// response.send(client);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Now, we can use `?` instead of `match`, and the return type makes a lot more sense: if the loop</span>
<span class="doccomment">/// ever stops, it means that an error occurred. We don't even have to wrap the loop in an `Ok`</span>
<span class="doccomment">/// because `!` coerces to `Result<!, ConnectionError>` automatically.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`String::from_str`]: str/trait.FromStr.html#tymethod.from_str</span>
<span class="doccomment">/// [`Result<String, !>`]: result/enum.Result.html</span>
<span class="doccomment">/// [`Result<T, !>`]: result/enum.Result.html</span>
<span class="doccomment">/// [`Result<!, E>`]: result/enum.Result.html</span>
<span class="doccomment">/// [`Ok`]: result/enum.Result.html#variant.Ok</span>
<span class="doccomment">/// [`String`]: string/struct.String.html</span>
<span class="doccomment">/// [`Err`]: result/enum.Result.html#variant.Err</span>
<span class="doccomment">/// [`FromStr`]: str/trait.FromStr.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # `!` and traits</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When writing your own traits, `!` should have an `impl` whenever there is an obvious `impl`</span>
<span class="doccomment">/// which doesn't `panic!`. As is turns out, most traits can have an `impl` for `!`. Take [`Debug`]</span>
<span class="doccomment">/// for example:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// #![feature(never_type)]</span>
<span class="doccomment">/// # use std::fmt;</span>
<span class="doccomment">/// # trait Debug {</span>
<span class="doccomment">/// # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result;</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// impl Debug for ! {</span>
<span class="doccomment">/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {</span>
<span class="doccomment">/// *self</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Once again we're using `!`'s ability to coerce into any other type, in this case</span>
<span class="doccomment">/// [`fmt::Result`]. Since this method takes a `&!` as an argument we know that it can never be</span>
<span class="doccomment">/// called (because there is no value of type `!` for it to be called with). Writing `*self`</span>
<span class="doccomment">/// essentially tells the compiler "We know that this code can never be run, so just treat the</span>
<span class="doccomment">/// entire function body has having type [`fmt::Result`]". This pattern can be used a lot when</span>
<span class="doccomment">/// implementing traits for `!`. Generally, any trait which only has methods which take a `self`</span>
<span class="doccomment">/// parameter should have such as impl.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// On the other hand, one trait which would not be appropriate to implement is [`Default`]:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// trait Default {</span>
<span class="doccomment">/// fn default() -> Self;</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Since `!` has no values, it has no default value either. It's true that we could write an</span>
<span class="doccomment">/// `impl` for this which simply panics, but the same is true for any type (we could `impl</span>
<span class="doccomment">/// Default` for (eg.) [`File`] by just making [`default()`] panic.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`fmt::Result`]: fmt/type.Result.html</span>
<span class="doccomment">/// [`File`]: fs/struct.File.html</span>
<span class="doccomment">/// [`Debug`]: fmt/trait.Debug.html</span>
<span class="doccomment">/// [`Default`]: default/trait.Default.html</span>
<span class="doccomment">/// [`default()`]: default/trait.Default.html#tymethod.default</span>
<span class="doccomment">///</span>
<span class="kw">mod</span> <span class="ident">prim_never</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"char"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// A character type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `char` type represents a single character. More specifically, since</span>
<span class="doccomment">/// 'character' isn't a well-defined concept in Unicode, `char` is a '[Unicode</span>
<span class="doccomment">/// scalar value]', which is similar to, but not the same as, a '[Unicode code</span>
<span class="doccomment">/// point]'.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [Unicode scalar value]: http://www.unicode.org/glossary/#unicode_scalar_value</span>
<span class="doccomment">/// [Unicode code point]: http://www.unicode.org/glossary/#code_point</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This documentation describes a number of methods and trait implementations on the</span>
<span class="doccomment">/// `char` type. For technical reasons, there is additional, separate</span>
<span class="doccomment">/// documentation in [the `std::char` module](char/index.html) as well.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Representation</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `char` is always four bytes in size. This is a different representation than</span>
<span class="doccomment">/// a given character would have as part of a [`String`]. For example:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let v = vec!['h', 'e', 'l', 'l', 'o'];</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // five elements times four bytes for each element</span>
<span class="doccomment">/// assert_eq!(20, v.len() * std::mem::size_of::<char>());</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let s = String::from("hello");</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // five elements times one byte per element</span>
<span class="doccomment">/// assert_eq!(5, s.len() * std::mem::size_of::<u8>());</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`String`]: string/struct.String.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// As always, remember that a human intuition for 'character' may not map to</span>
<span class="doccomment">/// Unicode's definitions. For example, despite looking similar, the 'é'</span>
<span class="doccomment">/// character is one Unicode code point while 'é' is two Unicode code points:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let mut chars = "é".chars();</span>
<span class="doccomment">/// // U+00e9: 'latin small letter e with acute'</span>
<span class="doccomment">/// assert_eq!(Some('\u{00e9}'), chars.next());</span>
<span class="doccomment">/// assert_eq!(None, chars.next());</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let mut chars = "é".chars();</span>
<span class="doccomment">/// // U+0065: 'latin small letter e'</span>
<span class="doccomment">/// assert_eq!(Some('\u{0065}'), chars.next());</span>
<span class="doccomment">/// // U+0301: 'combining acute accent'</span>
<span class="doccomment">/// assert_eq!(Some('\u{0301}'), chars.next());</span>
<span class="doccomment">/// assert_eq!(None, chars.next());</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This means that the contents of the first string above _will_ fit into a</span>
<span class="doccomment">/// `char` while the contents of the second string _will not_. Trying to create</span>
<span class="doccomment">/// a `char` literal with the contents of the second string gives an error:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```text</span>
<span class="doccomment">/// error: character literal may only contain one codepoint: 'é'</span>
<span class="doccomment">/// let c = 'é';</span>
<span class="doccomment">/// ^^^^</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Another implication of the 4-byte fixed size of a `char` is that</span>
<span class="doccomment">/// per-`char` processing can end up using a lot more memory:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let s = String::from("love: ❤️");</span>
<span class="doccomment">/// let v: Vec<char> = s.chars().collect();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(12, s.len() * std::mem::size_of::<u8>());</span>
<span class="doccomment">/// assert_eq!(32, v.len() * std::mem::size_of::<char>());</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">mod</span> <span class="ident">prim_char</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"unit"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The `()` type, sometimes called "unit" or "nil".</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `()` type has exactly one value `()`, and is used when there</span>
<span class="doccomment">/// is no other meaningful value that could be returned. `()` is most</span>
<span class="doccomment">/// commonly seen implicitly: functions without a `-> ...` implicitly</span>
<span class="doccomment">/// have return type `()`, that is, these are equivalent:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```rust</span>
<span class="doccomment">/// fn long() -> () {}</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn short() {}</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The semicolon `;` can be used to discard the result of an</span>
<span class="doccomment">/// expression at the end of a block, making the expression (and thus</span>
<span class="doccomment">/// the block) evaluate to `()`. For example,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```rust</span>
<span class="doccomment">/// fn returns_i64() -> i64 {</span>
<span class="doccomment">/// 1i64</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// fn returns_unit() {</span>
<span class="doccomment">/// 1i64;</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let is_i64 = {</span>
<span class="doccomment">/// returns_i64()</span>
<span class="doccomment">/// };</span>
<span class="doccomment">/// let is_unit = {</span>
<span class="doccomment">/// returns_i64();</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">mod</span> <span class="ident">prim_unit</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"pointer"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// Raw, unsafe pointers, `*const T`, and `*mut T`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::ptr` module](ptr/index.html).*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Working with raw pointers in Rust is uncommon,</span>
<span class="doccomment">/// typically limited to a few patterns.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Use the [`null`] and [`null_mut`] functions to create null pointers, and the</span>
<span class="doccomment">/// [`is_null`] method of the `*const T` and `*mut T` types to check for null.</span>
<span class="doccomment">/// The `*const T` and `*mut T` types also define the [`offset`] method, for</span>
<span class="doccomment">/// pointer math.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Common ways to create raw pointers</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ## 1. Coerce a reference (`&T`) or mutable reference (`&mut T`).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let my_num: i32 = 10;</span>
<span class="doccomment">/// let my_num_ptr: *const i32 = &my_num;</span>
<span class="doccomment">/// let mut my_speed: i32 = 88;</span>
<span class="doccomment">/// let my_speed_ptr: *mut i32 = &mut my_speed;</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// To get a pointer to a boxed value, dereference the box:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let my_num: Box<i32> = Box::new(10);</span>
<span class="doccomment">/// let my_num_ptr: *const i32 = &*my_num;</span>
<span class="doccomment">/// let mut my_speed: Box<i32> = Box::new(88);</span>
<span class="doccomment">/// let my_speed_ptr: *mut i32 = &mut *my_speed;</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This does not take ownership of the original allocation</span>
<span class="doccomment">/// and requires no resource management later,</span>
<span class="doccomment">/// but you must not use the pointer after its lifetime.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ## 2. Consume a box (`Box<T>`).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The [`into_raw`] function consumes a box and returns</span>
<span class="doccomment">/// the raw pointer. It doesn't destroy `T` or deallocate any memory.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let my_speed: Box<i32> = Box::new(88);</span>
<span class="doccomment">/// let my_speed: *mut i32 = Box::into_raw(my_speed);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // By taking ownership of the original `Box<T>` though</span>
<span class="doccomment">/// // we are obligated to put it together later to be destroyed.</span>
<span class="doccomment">/// unsafe {</span>
<span class="doccomment">/// drop(Box::from_raw(my_speed));</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that here the call to [`drop`] is for clarity - it indicates</span>
<span class="doccomment">/// that we are done with the given value and it should be destroyed.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ## 3. Get it from C.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # #![feature(libc)]</span>
<span class="doccomment">/// extern crate libc;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// use std::mem;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn main() {</span>
<span class="doccomment">/// unsafe {</span>
<span class="doccomment">/// let my_num: *mut i32 = libc::malloc(mem::size_of::<i32>()) as *mut i32;</span>
<span class="doccomment">/// if my_num.is_null() {</span>
<span class="doccomment">/// panic!("failed to allocate memory");</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// libc::free(my_num as *mut libc::c_void);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Usually you wouldn't literally use `malloc` and `free` from Rust,</span>
<span class="doccomment">/// but C APIs hand out a lot of pointers generally, so are a common source</span>
<span class="doccomment">/// of raw pointers in Rust.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`null`]: ../std/ptr/fn.null.html</span>
<span class="doccomment">/// [`null_mut`]: ../std/ptr/fn.null_mut.html</span>
<span class="doccomment">/// [`is_null`]: ../std/primitive.pointer.html#method.is_null</span>
<span class="doccomment">/// [`offset`]: ../std/primitive.pointer.html#method.offset</span>
<span class="doccomment">/// [`into_raw`]: ../std/boxed/struct.Box.html#method.into_raw</span>
<span class="doccomment">/// [`drop`]: ../std/mem/fn.drop.html</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">mod</span> <span class="ident">prim_pointer</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"array"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// A fixed-size array, denoted `[T; N]`, for the element type, `T`, and the</span>
<span class="doccomment">/// non-negative compile-time constant size, `N`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// There are two syntactic forms for creating an array:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * A list with each element, i.e. `[x, y, z]`.</span>
<span class="doccomment">/// * A repeat expression `[x; N]`, which produces an array with `N` copies of `x`.</span>
<span class="doccomment">/// The type of `x` must be [`Copy`][copy].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Arrays of sizes from 0 to 32 (inclusive) implement the following traits if</span>
<span class="doccomment">/// the element type allows it:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// - [`Debug`][debug]</span>
<span class="doccomment">/// - [`IntoIterator`][intoiterator] (implemented for `&[T; N]` and `&mut [T; N]`)</span>
<span class="doccomment">/// - [`PartialEq`][partialeq], [`PartialOrd`][partialord], [`Eq`][eq], [`Ord`][ord]</span>
<span class="doccomment">/// - [`Hash`][hash]</span>
<span class="doccomment">/// - [`AsRef`][asref], [`AsMut`][asmut]</span>
<span class="doccomment">/// - [`Borrow`][borrow], [`BorrowMut`][borrowmut]</span>
<span class="doccomment">/// - [`Default`][default]</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This limitation on the size `N` exists because Rust does not yet support</span>
<span class="doccomment">/// code that is generic over the size of an array type. `[Foo; 3]` and `[Bar; 3]`</span>
<span class="doccomment">/// are instances of same generic type `[T; 3]`, but `[Foo; 3]` and `[Foo; 5]` are</span>
<span class="doccomment">/// entirely different types. As a stopgap, trait implementations are</span>
<span class="doccomment">/// statically generated up to size 32.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Arrays of *any* size are [`Copy`][copy] if the element type is [`Copy`][copy]</span>
<span class="doccomment">/// and [`Clone`][clone] if the element type is [`Clone`][clone]. This works</span>
<span class="doccomment">/// because [`Copy`][copy] and [`Clone`][clone] traits are specially known</span>
<span class="doccomment">/// to the compiler.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Arrays coerce to [slices (`[T]`)][slice], so a slice method may be called on</span>
<span class="doccomment">/// an array. Indeed, this provides most of the API for working with arrays.</span>
<span class="doccomment">/// Slices have a dynamic size and do not coerce to arrays.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// There is no way to move elements out of an array. See [`mem::replace`][replace]</span>
<span class="doccomment">/// for an alternative.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let mut array: [i32; 3] = [0; 3];</span>
<span class="doccomment">///</span>
<span class="doccomment">/// array[1] = 1;</span>
<span class="doccomment">/// array[2] = 2;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!([1, 2], &array[1..]);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // This loop prints: 0 1 2</span>
<span class="doccomment">/// for x in &array {</span>
<span class="doccomment">/// print!("{} ", x);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// An array itself is not iterable:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```compile_fail,E0277</span>
<span class="doccomment">/// let array: [i32; 3] = [0; 3];</span>
<span class="doccomment">///</span>
<span class="doccomment">/// for x in array { }</span>
<span class="doccomment">/// // error: the trait bound `[i32; 3]: std::iter::Iterator` is not satisfied</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The solution is to coerce the array to a slice by calling a slice method:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # let array: [i32; 3] = [0; 3];</span>
<span class="doccomment">/// for x in array.iter() { }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If the array has 32 or fewer elements (see above), you can also use the</span>
<span class="doccomment">/// array reference's [`IntoIterator`] implementation:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # let array: [i32; 3] = [0; 3];</span>
<span class="doccomment">/// for x in &array { }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [slice]: primitive.slice.html</span>
<span class="doccomment">/// [copy]: marker/trait.Copy.html</span>
<span class="doccomment">/// [clone]: clone/trait.Clone.html</span>
<span class="doccomment">/// [debug]: fmt/trait.Debug.html</span>
<span class="doccomment">/// [intoiterator]: iter/trait.IntoIterator.html</span>
<span class="doccomment">/// [partialeq]: cmp/trait.PartialEq.html</span>
<span class="doccomment">/// [partialord]: cmp/trait.PartialOrd.html</span>
<span class="doccomment">/// [eq]: cmp/trait.Eq.html</span>
<span class="doccomment">/// [ord]: cmp/trait.Ord.html</span>
<span class="doccomment">/// [hash]: hash/trait.Hash.html</span>
<span class="doccomment">/// [asref]: convert/trait.AsRef.html</span>
<span class="doccomment">/// [asmut]: convert/trait.AsMut.html</span>
<span class="doccomment">/// [borrow]: borrow/trait.Borrow.html</span>
<span class="doccomment">/// [borrowmut]: borrow/trait.BorrowMut.html</span>
<span class="doccomment">/// [default]: default/trait.Default.html</span>
<span class="doccomment">/// [replace]: mem/fn.replace.html</span>
<span class="doccomment">/// [`IntoIterator`]: iter/trait.IntoIterator.html</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">mod</span> <span class="ident">prim_array</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"slice"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"["</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"]"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"[]"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// A dynamically-sized view into a contiguous sequence, `[T]`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::slice` module](slice/index.html).*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Slices are a view into a block of memory represented as a pointer and a</span>
<span class="doccomment">/// length.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// // slicing a Vec</span>
<span class="doccomment">/// let vec = vec![1, 2, 3];</span>
<span class="doccomment">/// let int_slice = &vec[..];</span>
<span class="doccomment">/// // coercing an array to a slice</span>
<span class="doccomment">/// let str_slice: &[&str] = &["one", "two", "three"];</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Slices are either mutable or shared. The shared slice type is `&[T]`,</span>
<span class="doccomment">/// while the mutable slice type is `&mut [T]`, where `T` represents the element</span>
<span class="doccomment">/// type. For example, you can mutate the block of memory that a mutable slice</span>
<span class="doccomment">/// points to:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let x = &mut [1, 2, 3];</span>
<span class="doccomment">/// x[1] = 7;</span>
<span class="doccomment">/// assert_eq!(x, &[1, 7, 3]);</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">mod</span> <span class="ident">prim_slice</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"str"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// String slices.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::str` module](str/index.html).*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `str` type, also called a 'string slice', is the most primitive string</span>
<span class="doccomment">/// type. It is usually seen in its borrowed form, `&str`. It is also the type</span>
<span class="doccomment">/// of string literals, `&'static str`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// String slices are always valid UTF-8.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// String literals are string slices:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let hello = "Hello, world!";</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // with an explicit type annotation</span>
<span class="doccomment">/// let hello: &'static str = "Hello, world!";</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// They are `'static` because they're stored directly in the final binary, and</span>
<span class="doccomment">/// so will be valid for the `'static` duration.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Representation</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A `&str` is made up of two components: a pointer to some bytes, and a</span>
<span class="doccomment">/// length. You can look at these with the [`as_ptr`] and [`len`] methods:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::slice;</span>
<span class="doccomment">/// use std::str;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let story = "Once upon a time...";</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let ptr = story.as_ptr();</span>
<span class="doccomment">/// let len = story.len();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // story has nineteen bytes</span>
<span class="doccomment">/// assert_eq!(19, len);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // We can re-build a str out of ptr and len. This is all unsafe because</span>
<span class="doccomment">/// // we are responsible for making sure the two components are valid:</span>
<span class="doccomment">/// let s = unsafe {</span>
<span class="doccomment">/// // First, we build a &[u8]...</span>
<span class="doccomment">/// let slice = slice::from_raw_parts(ptr, len);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // ... and then convert that slice into a string slice</span>
<span class="doccomment">/// str::from_utf8(slice)</span>
<span class="doccomment">/// };</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(s, Ok(story));</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`as_ptr`]: #method.as_ptr</span>
<span class="doccomment">/// [`len`]: #method.len</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note: This example shows the internals of `&str`. `unsafe` should not be</span>
<span class="doccomment">/// used to get a string slice under normal circumstances. Use `as_slice`</span>
<span class="doccomment">/// instead.</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">mod</span> <span class="ident">prim_str</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"tuple"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"("</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">")"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"()"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// A finite heterogeneous sequence, `(T, U, ..)`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Let's cover each of those in turn:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Tuples are *finite*. In other words, a tuple has a length. Here's a tuple</span>
<span class="doccomment">/// of length `3`:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// ("hello", 5, 'c');</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// 'Length' is also sometimes called 'arity' here; each tuple of a different</span>
<span class="doccomment">/// length is a different, distinct type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Tuples are *heterogeneous*. This means that each element of the tuple can</span>
<span class="doccomment">/// have a different type. In that tuple above, it has the type:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # let _:</span>
<span class="doccomment">/// (&'static str, i32, char)</span>
<span class="doccomment">/// # = ("hello", 5, 'c');</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Tuples are a *sequence*. This means that they can be accessed by position;</span>
<span class="doccomment">/// this is called 'tuple indexing', and it looks like this:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```rust</span>
<span class="doccomment">/// let tuple = ("hello", 5, 'c');</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(tuple.0, "hello");</span>
<span class="doccomment">/// assert_eq!(tuple.1, 5);</span>
<span class="doccomment">/// assert_eq!(tuple.2, 'c');</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For more about tuples, see [the book](../book/first-edition/primitive-types.html#tuples).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Trait implementations</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If every type inside a tuple implements one of the following traits, then a</span>
<span class="doccomment">/// tuple itself also implements it.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * [`Clone`]</span>
<span class="doccomment">/// * [`Copy`]</span>
<span class="doccomment">/// * [`PartialEq`]</span>
<span class="doccomment">/// * [`Eq`]</span>
<span class="doccomment">/// * [`PartialOrd`]</span>
<span class="doccomment">/// * [`Ord`]</span>
<span class="doccomment">/// * [`Debug`]</span>
<span class="doccomment">/// * [`Default`]</span>
<span class="doccomment">/// * [`Hash`]</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Clone`]: clone/trait.Clone.html</span>
<span class="doccomment">/// [`Copy`]: marker/trait.Copy.html</span>
<span class="doccomment">/// [`PartialEq`]: cmp/trait.PartialEq.html</span>
<span class="doccomment">/// [`Eq`]: cmp/trait.Eq.html</span>
<span class="doccomment">/// [`PartialOrd`]: cmp/trait.PartialOrd.html</span>
<span class="doccomment">/// [`Ord`]: cmp/trait.Ord.html</span>
<span class="doccomment">/// [`Debug`]: fmt/trait.Debug.html</span>
<span class="doccomment">/// [`Default`]: default/trait.Default.html</span>
<span class="doccomment">/// [`Hash`]: hash/trait.Hash.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Due to a temporary restriction in Rust's type system, these traits are only</span>
<span class="doccomment">/// implemented on tuples of arity 12 or less. In the future, this may change.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Basic usage:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let tuple = ("hello", 5, 'c');</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(tuple.0, "hello");</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Tuples are often used as a return type when you want to return more than</span>
<span class="doccomment">/// one value:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// fn calculate_point() -> (i32, i32) {</span>
<span class="doccomment">/// // Don't do a calculation, that's not the point of the example</span>
<span class="doccomment">/// (4, 5)</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let point = calculate_point();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(point.0, 4);</span>
<span class="doccomment">/// assert_eq!(point.1, 5);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Combining this with patterns can be nicer.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let (x, y) = calculate_point();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(x, 4);</span>
<span class="doccomment">/// assert_eq!(y, 5);</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">mod</span> <span class="ident">prim_tuple</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"f32"</span>)]</span>
<span class="doccomment">/// The 32-bit floating point type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::f32` module](f32/index.html).*</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">mod</span> <span class="ident">prim_f32</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"f64"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 64-bit floating point type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::f64` module](f64/index.html).*</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">mod</span> <span class="ident">prim_f64</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"i8"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 8-bit signed integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::i8` module](i8/index.html).*</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">mod</span> <span class="ident">prim_i8</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"i16"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 16-bit signed integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::i16` module](i16/index.html).*</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">mod</span> <span class="ident">prim_i16</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"i32"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 32-bit signed integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::i32` module](i32/index.html).*</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">mod</span> <span class="ident">prim_i32</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"i64"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 64-bit signed integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::i64` module](i64/index.html).*</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">mod</span> <span class="ident">prim_i64</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"i128"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 128-bit signed integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::i128` module](i128/index.html).*</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"i128"</span>, <span class="ident">since</span><span class="op">=</span><span class="string">"1.26.0"</span>)]</span>
<span class="kw">mod</span> <span class="ident">prim_i128</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"u8"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 8-bit unsigned integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::u8` module](u8/index.html).*</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">mod</span> <span class="ident">prim_u8</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"u16"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 16-bit unsigned integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::u16` module](u16/index.html).*</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">mod</span> <span class="ident">prim_u16</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"u32"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 32-bit unsigned integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::u32` module](u32/index.html).*</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">mod</span> <span class="ident">prim_u32</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"u64"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 64-bit unsigned integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::u64` module](u64/index.html).*</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">mod</span> <span class="ident">prim_u64</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"u128"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The 128-bit unsigned integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::u128` module](u128/index.html).*</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"i128"</span>, <span class="ident">since</span><span class="op">=</span><span class="string">"1.26.0"</span>)]</span>
<span class="kw">mod</span> <span class="ident">prim_u128</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"isize"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The pointer-sized signed integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::isize` module](isize/index.html).*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The size of this primitive is how many bytes it takes to reference any</span>
<span class="doccomment">/// location in memory. For example, on a 32 bit target, this is 4 bytes</span>
<span class="doccomment">/// and on a 64 bit target, this is 8 bytes.</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">mod</span> <span class="ident">prim_isize</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"usize"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// The pointer-sized unsigned integer type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *[See also the `std::usize` module](usize/index.html).*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The size of this primitive is how many bytes it takes to reference any</span>
<span class="doccomment">/// location in memory. For example, on a 32 bit target, this is 4 bytes</span>
<span class="doccomment">/// and on a 64 bit target, this is 8 bytes.</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">mod</span> <span class="ident">prim_usize</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"reference"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">alias</span> <span class="op">=</span> <span class="string">"&"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// References, both shared and mutable.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A reference represents a borrow of some owned value. You can get one by using the `&` or `&mut`</span>
<span class="doccomment">/// operators on a value, or by using a `ref` or `ref mut` pattern.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For those familiar with pointers, a reference is just a pointer that is assumed to not be null.</span>
<span class="doccomment">/// In fact, `Option<&T>` has the same memory representation as a nullable pointer, and can be</span>
<span class="doccomment">/// passed across FFI boundaries as such.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In most cases, references can be used much like the original value. Field access, method</span>
<span class="doccomment">/// calling, and indexing work the same (save for mutability rules, of course). In addition, the</span>
<span class="doccomment">/// comparison operators transparently defer to the referent's implementation, allowing references</span>
<span class="doccomment">/// to be compared the same as owned values.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// References have a lifetime attached to them, which represents the scope for which the borrow is</span>
<span class="doccomment">/// valid. A lifetime is said to "outlive" another one if its representative scope is as long or</span>
<span class="doccomment">/// longer than the other. The `'static` lifetime is the longest lifetime, which represents the</span>
<span class="doccomment">/// total life of the program. For example, string literals have a `'static` lifetime because the</span>
<span class="doccomment">/// text data is embedded into the binary of the program, rather than in an allocation that needs</span>
<span class="doccomment">/// to be dynamically managed.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `&mut T` references can be freely coerced into `&T` references with the same referent type, and</span>
<span class="doccomment">/// references with longer lifetimes can be freely coerced into references with shorter ones.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For more information on how to use references, see [the book's section on "References and</span>
<span class="doccomment">/// Borrowing"][book-refs].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [book-refs]: ../book/second-edition/ch04-02-references-and-borrowing.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The following traits are implemented for all `&T`, regardless of the type of its referent:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * [`Copy`]</span>
<span class="doccomment">/// * [`Clone`] \(Note that this will not defer to `T`'s `Clone` implementation if it exists!)</span>
<span class="doccomment">/// * [`Deref`]</span>
<span class="doccomment">/// * [`Borrow`]</span>
<span class="doccomment">/// * [`Pointer`]</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Copy`]: marker/trait.Copy.html</span>
<span class="doccomment">/// [`Clone`]: clone/trait.Clone.html</span>
<span class="doccomment">/// [`Deref`]: ops/trait.Deref.html</span>
<span class="doccomment">/// [`Borrow`]: borrow/trait.Borrow.html</span>
<span class="doccomment">/// [`Pointer`]: fmt/trait.Pointer.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `&mut T` references get all of the above except `Copy` and `Clone` (to prevent creating</span>
<span class="doccomment">/// multiple simultaneous mutable borrows), plus the following, regardless of the type of its</span>
<span class="doccomment">/// referent:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * [`DerefMut`]</span>
<span class="doccomment">/// * [`BorrowMut`]</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`DerefMut`]: ops/trait.DerefMut.html</span>
<span class="doccomment">/// [`BorrowMut`]: borrow/trait.BorrowMut.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The following traits are implemented on `&T` references if the underlying `T` also implements</span>
<span class="doccomment">/// that trait:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * All the traits in [`std::fmt`] except [`Pointer`] and [`fmt::Write`]</span>
<span class="doccomment">/// * [`PartialOrd`]</span>
<span class="doccomment">/// * [`Ord`]</span>
<span class="doccomment">/// * [`PartialEq`]</span>
<span class="doccomment">/// * [`Eq`]</span>
<span class="doccomment">/// * [`AsRef`]</span>
<span class="doccomment">/// * [`Fn`] \(in addition, `&T` references get [`FnMut`] and [`FnOnce`] if `T: Fn`)</span>
<span class="doccomment">/// * [`Hash`]</span>
<span class="doccomment">/// * [`ToSocketAddrs`]</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`std::fmt`]: fmt/index.html</span>
<span class="doccomment">/// [`fmt::Write`]: fmt/trait.Write.html</span>
<span class="doccomment">/// [`PartialOrd`]: cmp/trait.PartialOrd.html</span>
<span class="doccomment">/// [`Ord`]: cmp/trait.Ord.html</span>
<span class="doccomment">/// [`PartialEq`]: cmp/trait.PartialEq.html</span>
<span class="doccomment">/// [`Eq`]: cmp/trait.Eq.html</span>
<span class="doccomment">/// [`AsRef`]: convert/trait.AsRef.html</span>
<span class="doccomment">/// [`Fn`]: ops/trait.Fn.html</span>
<span class="doccomment">/// [`FnMut`]: ops/trait.FnMut.html</span>
<span class="doccomment">/// [`FnOnce`]: ops/trait.FnOnce.html</span>
<span class="doccomment">/// [`Hash`]: hash/trait.Hash.html</span>
<span class="doccomment">/// [`ToSocketAddrs`]: net/trait.ToSocketAddrs.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `&mut T` references get all of the above except `ToSocketAddrs`, plus the following, if `T`</span>
<span class="doccomment">/// implements that trait:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * [`AsMut`]</span>
<span class="doccomment">/// * [`FnMut`] \(in addition, `&mut T` references get [`FnOnce`] if `T: FnMut`)</span>
<span class="doccomment">/// * [`fmt::Write`]</span>
<span class="doccomment">/// * [`Iterator`]</span>
<span class="doccomment">/// * [`DoubleEndedIterator`]</span>
<span class="doccomment">/// * [`ExactSizeIterator`]</span>
<span class="doccomment">/// * [`FusedIterator`]</span>
<span class="doccomment">/// * [`TrustedLen`]</span>
<span class="doccomment">/// * [`Send`] \(note that `&T` references only get `Send` if `T: Sync`)</span>
<span class="doccomment">/// * [`io::Write`]</span>
<span class="doccomment">/// * [`Read`]</span>
<span class="doccomment">/// * [`Seek`]</span>
<span class="doccomment">/// * [`BufRead`]</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`AsMut`]: convert/trait.AsMut.html</span>
<span class="doccomment">/// [`Iterator`]: iter/trait.Iterator.html</span>
<span class="doccomment">/// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html</span>
<span class="doccomment">/// [`ExactSizeIterator`]: iter/trait.ExactSizeIterator.html</span>
<span class="doccomment">/// [`FusedIterator`]: iter/trait.FusedIterator.html</span>
<span class="doccomment">/// [`TrustedLen`]: iter/trait.TrustedLen.html</span>
<span class="doccomment">/// [`Send`]: marker/trait.Send.html</span>
<span class="doccomment">/// [`io::Write`]: io/trait.Write.html</span>
<span class="doccomment">/// [`Read`]: io/trait.Read.html</span>
<span class="doccomment">/// [`Seek`]: io/trait.Seek.html</span>
<span class="doccomment">/// [`BufRead`]: io/trait.BufRead.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that due to method call deref coercion, simply calling a trait method will act like they</span>
<span class="doccomment">/// work on references as well as they do on owned values! The implementations described here are</span>
<span class="doccomment">/// meant for generic contexts, where the final type `T` is a type parameter or otherwise not</span>
<span class="doccomment">/// locally known.</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">mod</span> <span class="ident">prim_ref</span> { }
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">primitive</span> <span class="op">=</span> <span class="string">"fn"</span>)]</span>
<span class="comment">//</span>
<span class="doccomment">/// Function pointers, like `fn(usize) -> bool`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *See also the traits [`Fn`], [`FnMut`], and [`FnOnce`].*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Fn`]: ops/trait.Fn.html</span>
<span class="doccomment">/// [`FnMut`]: ops/trait.FnMut.html</span>
<span class="doccomment">/// [`FnOnce`]: ops/trait.FnOnce.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Plain function pointers are obtained by casting either plain functions, or closures that don't</span>
<span class="doccomment">/// capture an environment:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// fn add_one(x: usize) -> usize {</span>
<span class="doccomment">/// x + 1</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let ptr: fn(usize) -> usize = add_one;</span>
<span class="doccomment">/// assert_eq!(ptr(5), 6);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let clos: fn(usize) -> usize = |x| x + 5;</span>
<span class="doccomment">/// assert_eq!(clos(5), 10);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In addition to varying based on their signature, function pointers come in two flavors: safe</span>
<span class="doccomment">/// and unsafe. Plain `fn()` function pointers can only point to safe functions,</span>
<span class="doccomment">/// while `unsafe fn()` function pointers can point to safe or unsafe functions.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// fn add_one(x: usize) -> usize {</span>
<span class="doccomment">/// x + 1</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// unsafe fn add_one_unsafely(x: usize) -> usize {</span>
<span class="doccomment">/// x + 1</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let safe_ptr: fn(usize) -> usize = add_one;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// //ERROR: mismatched types: expected normal fn, found unsafe fn</span>
<span class="doccomment">/// //let bad_ptr: fn(usize) -> usize = add_one_unsafely;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let unsafe_ptr: unsafe fn(usize) -> usize = add_one_unsafely;</span>
<span class="doccomment">/// let really_safe_ptr: unsafe fn(usize) -> usize = add_one;</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// On top of that, function pointers can vary based on what ABI they use. This is achieved by</span>
<span class="doccomment">/// adding the `extern` keyword to the type name, followed by the ABI in question. For example,</span>
<span class="doccomment">/// `fn()` is different from `extern "C" fn()`, which itself is different from `extern "stdcall"</span>
<span class="doccomment">/// fn()`, and so on for the various ABIs that Rust supports. Non-`extern` functions have an ABI</span>
<span class="doccomment">/// of `"Rust"`, and `extern` functions without an explicit ABI have an ABI of `"C"`. For more</span>
<span class="doccomment">/// information, see [the nomicon's section on foreign calling conventions][nomicon-abi].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [nomicon-abi]: ../nomicon/ffi.html#foreign-calling-conventions</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Extern function declarations with the "C" or "cdecl" ABIs can also be *variadic*, allowing them</span>
<span class="doccomment">/// to be called with a variable number of arguments. Normal rust functions, even those with an</span>
<span class="doccomment">/// `extern "ABI"`, cannot be variadic. For more information, see [the nomicon's section on</span>
<span class="doccomment">/// variadic functions][nomicon-variadic].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [nomicon-variadic]: ../nomicon/ffi.html#variadic-functions</span>
<span class="doccomment">///</span>
<span class="doccomment">/// These markers can be combined, so `unsafe extern "stdcall" fn()` is a valid type.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Like references in rust, function pointers are assumed to not be null, so if you want to pass a</span>
<span class="doccomment">/// function pointer over FFI and be able to accommodate null pointers, make your type</span>
<span class="doccomment">/// `Option<fn()>` with your required signature.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Function pointers implement the following traits:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * [`Clone`]</span>
<span class="doccomment">/// * [`PartialEq`]</span>
<span class="doccomment">/// * [`Eq`]</span>
<span class="doccomment">/// * [`PartialOrd`]</span>
<span class="doccomment">/// * [`Ord`]</span>
<span class="doccomment">/// * [`Hash`]</span>
<span class="doccomment">/// * [`Pointer`]</span>
<span class="doccomment">/// * [`Debug`]</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Clone`]: clone/trait.Clone.html</span>
<span class="doccomment">/// [`PartialEq`]: cmp/trait.PartialEq.html</span>
<span class="doccomment">/// [`Eq`]: cmp/trait.Eq.html</span>
<span class="doccomment">/// [`PartialOrd`]: cmp/trait.PartialOrd.html</span>
<span class="doccomment">/// [`Ord`]: cmp/trait.Ord.html</span>
<span class="doccomment">/// [`Hash`]: hash/trait.Hash.html</span>
<span class="doccomment">/// [`Pointer`]: fmt/trait.Pointer.html</span>
<span class="doccomment">/// [`Debug`]: fmt/trait.Debug.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Due to a temporary restriction in Rust's type system, these traits are only implemented on</span>
<span class="doccomment">/// functions that take 12 arguments or less, with the `"Rust"` and `"C"` ABIs. In the future, this</span>
<span class="doccomment">/// may change.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In addition, function pointers of *any* signature, ABI, or safety are [`Copy`], and all *safe*</span>
<span class="doccomment">/// function pointers implement [`Fn`], [`FnMut`], and [`FnOnce`]. This works because these traits</span>
<span class="doccomment">/// are specially known to the compiler.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Copy`]: marker/trait.Copy.html</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">mod</span> <span class="ident">prim_fn</span> { }
</pre>
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