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</pre><pre class="rust ">
<span class="comment">// Copyright 2012 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">/// A trait for customizing the behavior of the `?` operator.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A type implementing `Try` is one that has a canonical way to view it</span>
<span class="doccomment">/// in terms of a success/failure dichotomy. This trait allows both</span>
<span class="doccomment">/// extracting those success or failure values from an existing instance and</span>
<span class="doccomment">/// creating a new instance from a success or failure value.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_trait"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"42327"</span>)]</span>
<span class="attribute">#[<span class="ident">rustc_on_unimplemented</span>(
<span class="ident">on</span>(<span class="ident">all</span>(
<span class="ident">any</span>(<span class="ident">from_method</span><span class="op">=</span><span class="string">"from_error"</span>, <span class="ident">from_method</span><span class="op">=</span><span class="string">"from_ok"</span>),
<span class="ident">from_desugaring</span><span class="op">=</span><span class="string">"?"</span>),
<span class="ident">message</span><span class="op">=</span><span class="string">"the `?` operator can only be used in a \
function that returns `Result` \
(or another type that implements `{Try}`)"</span>,
<span class="ident">label</span><span class="op">=</span><span class="string">"cannot use the `?` operator in a function that returns `{Self}`"</span>),
<span class="ident">on</span>(<span class="ident">all</span>(<span class="ident">from_method</span><span class="op">=</span><span class="string">"into_result"</span>, <span class="ident">from_desugaring</span><span class="op">=</span><span class="string">"?"</span>),
<span class="ident">message</span><span class="op">=</span><span class="string">"the `?` operator can only be applied to values \
that implement `{Try}`"</span>,
<span class="ident">label</span><span class="op">=</span><span class="string">"the `?` operator cannot be applied to type `{Self}`"</span>)
)]</span>
<span class="kw">pub</span> <span class="kw">trait</span> <span class="ident">Try</span> {
<span class="doccomment">/// The type of this value when viewed as successful.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_trait"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"42327"</span>)]</span>
<span class="kw">type</span> <span class="prelude-val">Ok</span>;
<span class="doccomment">/// The type of this value when viewed as failed.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_trait"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"42327"</span>)]</span>
<span class="kw">type</span> <span class="ident">Error</span>;
<span class="doccomment">/// Applies the "?" operator. A return of `Ok(t)` means that the</span>
<span class="doccomment">/// execution should continue normally, and the result of `?` is the</span>
<span class="doccomment">/// value `t`. A return of `Err(e)` means that execution should branch</span>
<span class="doccomment">/// to the innermost enclosing `catch`, or return from the function.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If an `Err(e)` result is returned, the value `e` will be "wrapped"</span>
<span class="doccomment">/// in the return type of the enclosing scope (which must itself implement</span>
<span class="doccomment">/// `Try`). Specifically, the value `X::from_error(From::from(e))`</span>
<span class="doccomment">/// is returned, where `X` is the return type of the enclosing function.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_trait"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"42327"</span>)]</span>
<span class="kw">fn</span> <span class="ident">into_result</span>(<span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="self">Self</span>::<span class="prelude-val">Ok</span>, <span class="self">Self</span>::<span class="ident">Error</span><span class="op">></span>;
<span class="doccomment">/// Wrap an error value to construct the composite result. For example,</span>
<span class="doccomment">/// `Result::Err(x)` and `Result::from_error(x)` are equivalent.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_trait"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"42327"</span>)]</span>
<span class="kw">fn</span> <span class="ident">from_error</span>(<span class="ident">v</span>: <span class="self">Self</span>::<span class="ident">Error</span>) <span class="op">-></span> <span class="self">Self</span>;
<span class="doccomment">/// Wrap an OK value to construct the composite result. For example,</span>
<span class="doccomment">/// `Result::Ok(x)` and `Result::from_ok(x)` are equivalent.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_trait"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"42327"</span>)]</span>
<span class="kw">fn</span> <span class="ident">from_ok</span>(<span class="ident">v</span>: <span class="self">Self</span>::<span class="prelude-val">Ok</span>) <span class="op">-></span> <span class="self">Self</span>;
}
</pre>
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