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<p class='location'>Module any</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li><li><a href="#traits">Traits</a></li></ul></div><p class='location'><a href='../index.html'>core</a></p><script>window.sidebarCurrent = {name: 'any', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div>
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<h1 class='fqn'><span class='in-band'>Module <a href='../index.html'>core</a>::<wbr><a class="mod" href=''>any</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'>
<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
[<span class='inner'>−</span>]
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</span><a class='srclink' href='../../src/core/any.rs.html#11-402' title='goto source code'>[src]</a></span></h1>
<div class='docblock'><p>This module implements the <code>Any</code> trait, which enables dynamic typing
of any <code>'static</code> type through runtime reflection.</p>
<p><code>Any</code> itself can be used to get a <code>TypeId</code>, and has more features when used
as a trait object. As <code>&Any</code> (a borrowed trait object), it has the <code>is</code> and
<code>downcast_ref</code> methods, to test if the contained value is of a given type,
and to get a reference to the inner value as a type. As <code>&mut Any</code>, there
is also the <code>downcast_mut</code> method, for getting a mutable reference to the
inner value. <code>Box<Any></code> adds the <code>downcast</code> method, which attempts to
convert to a <code>Box<T></code>. See the <a href="../../std/boxed/struct.Box.html"><code>Box</code></a> documentation for the full details.</p>
<p>Note that &Any is limited to testing whether a value is of a specified
concrete type, and cannot be used to test whether a type implements a trait.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Consider a situation where we want to log out a value passed to a function.
We know the value we're working on implements Debug, but we don't know its
concrete type. We want to give special treatment to certain types: in this
case printing out the length of String values prior to their value.
We don't know the concrete type of our value at compile time, so we need to
use runtime reflection instead.</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>::<span class="ident">Debug</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">any</span>::<span class="ident">Any</span>;
<span class="comment">// Logger function for any type that implements Debug.</span>
<span class="kw">fn</span> <span class="ident">log</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Any</span> <span class="op">+</span> <span class="ident">Debug</span><span class="op">></span>(<span class="ident">value</span>: <span class="kw-2">&</span><span class="ident">T</span>) {
<span class="kw">let</span> <span class="ident">value_any</span> <span class="op">=</span> <span class="ident">value</span> <span class="kw">as</span> <span class="kw-2">&</span><span class="ident">Any</span>;
<span class="comment">// try to convert our value to a String. If successful, we want to</span>
<span class="comment">// output the String's length as well as its value. If not, it's a</span>
<span class="comment">// different type: just print it out unadorned.</span>
<span class="kw">match</span> <span class="ident">value_any</span>.<span class="ident">downcast_ref</span>::<span class="op"><</span><span class="ident">String</span><span class="op">></span>() {
<span class="prelude-val">Some</span>(<span class="ident">as_string</span>) <span class="op">=></span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"String ({}): {}"</span>, <span class="ident">as_string</span>.<span class="ident">len</span>(), <span class="ident">as_string</span>);
}
<span class="prelude-val">None</span> <span class="op">=></span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{:?}"</span>, <span class="ident">value</span>);
}
}
}
<span class="comment">// This function wants to log its parameter out prior to doing work with it.</span>
<span class="kw">fn</span> <span class="ident">do_work</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Any</span> <span class="op">+</span> <span class="ident">Debug</span><span class="op">></span>(<span class="ident">value</span>: <span class="kw-2">&</span><span class="ident">T</span>) {
<span class="ident">log</span>(<span class="ident">value</span>);
<span class="comment">// ...do some other work</span>
}
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">my_string</span> <span class="op">=</span> <span class="string">"Hello World"</span>.<span class="ident">to_string</span>();
<span class="ident">do_work</span>(<span class="kw-2">&</span><span class="ident">my_string</span>);
<span class="kw">let</span> <span class="ident">my_i8</span>: <span class="ident">i8</span> <span class="op">=</span> <span class="number">100</span>;
<span class="ident">do_work</span>(<span class="kw-2">&</span><span class="ident">my_i8</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Ause%20std%3A%3Afmt%3A%3ADebug%3B%0Ause%20std%3A%3Aany%3A%3AAny%3B%0A%0A%2F%2F%20Logger%20function%20for%20any%20type%20that%20implements%20Debug.%0Afn%20log%3CT%3A%20Any%20%2B%20Debug%3E(value%3A%20%26T)%20%7B%0A%20%20%20%20let%20value_any%20%3D%20value%20as%20%26Any%3B%0A%0A%20%20%20%20%2F%2F%20try%20to%20convert%20our%20value%20to%20a%20String.%20%20If%20successful%2C%20we%20want%20to%0A%20%20%20%20%2F%2F%20output%20the%20String's%20length%20as%20well%20as%20its%20value.%20%20If%20not%2C%20it's%20a%0A%20%20%20%20%2F%2F%20different%20type%3A%20just%20print%20it%20out%20unadorned.%0A%20%20%20%20match%20value_any.downcast_ref%3A%3A%3CString%3E()%20%7B%0A%20%20%20%20%20%20%20%20Some(as_string)%20%3D%3E%20%7B%0A%20%20%20%20%20%20%20%20%20%20%20%20println!(%22String%20(%7B%7D)%3A%20%7B%7D%22%2C%20as_string.len()%2C%20as_string)%3B%0A%20%20%20%20%20%20%20%20%7D%0A%20%20%20%20%20%20%20%20None%20%3D%3E%20%7B%0A%20%20%20%20%20%20%20%20%20%20%20%20println!(%22%7B%3A%3F%7D%22%2C%20value)%3B%0A%20%20%20%20%20%20%20%20%7D%0A%20%20%20%20%7D%0A%7D%0A%0A%2F%2F%20This%20function%20wants%20to%20log%20its%20parameter%20out%20prior%20to%20doing%20work%20with%20it.%0Afn%20do_work%3CT%3A%20Any%20%2B%20Debug%3E(value%3A%20%26T)%20%7B%0A%20%20%20%20log(value)%3B%0A%20%20%20%20%2F%2F%20...do%20some%20other%20work%0A%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20my_string%20%3D%20%22Hello%20World%22.to_string()%3B%0A%20%20%20%20do_work(%26my_string)%3B%0A%0A%20%20%20%20let%20my_i8%3A%20i8%20%3D%20100%3B%0A%20%20%20%20do_work(%26my_i8)%3B%0A%7D%0A">Run</a></pre>
</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
<table>
<tr class=' module-item'>
<td><a class="struct" href="struct.TypeId.html"
title='struct core::any::TypeId'>TypeId</a></td>
<td class='docblock-short'>
<p>A <code>TypeId</code> represents a globally unique identifier for a type.</p>
</td>
</tr></table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
<table>
<tr class=' module-item'>
<td><a class="trait" href="trait.Any.html"
title='trait core::any::Any'>Any</a></td>
<td class='docblock-short'>
<p>A type to emulate dynamic typing.</p>
</td>
</tr></table></section>
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