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<h1 class='fqn'><span class='in-band'>Trait <a href='../index.html'>std</a>::<wbr><a href='index.html'>marker</a>::<wbr><a class="trait" href=''>Unsize</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version '></span><span id='render-detail'>
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<pre class='rust trait'><div class="docblock attributes">#[lang = "unsize"]
</div>pub trait Unsize<T> <span class="where fmt-newline">where<br> T: ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span>{ }</pre><div class='stability'><div class='stab unstable'><span class=microscope>🔬</span> This is a nightly-only experimental API. (<code>unsize </code><a href="https://github.com/rust-lang/rust/issues/27732">#27732</a>)</div></div><div class='docblock'><p>Types that can be "unsized" to a dynamically-sized type.</p>
<p>For example, the sized array type <code>[i8; 2]</code> implements <code>Unsize<[i8]></code> and
<code>Unsize<fmt::Debug></code>.</p>
<p>All implementations of <code>Unsize</code> are provided automatically by the compiler.</p>
<p><code>Unsize</code> is implemented for:</p>
<ul>
<li><code>[T; N]</code> is <code>Unsize<[T]></code></li>
<li><code>T</code> is <code>Unsize<Trait></code> when <code>T: Trait</code></li>
<li><code>Foo<..., T, ...></code> is <code>Unsize<Foo<..., U, ...>></code> if:
<ul>
<li><code>T: Unsize<U></code></li>
<li>Foo is a struct</li>
<li>Only the last field of <code>Foo</code> has a type involving <code>T</code></li>
<li><code>T</code> is not part of the type of any other fields</li>
<li><code>Bar<T>: Unsize<Bar<U>></code>, if the last field of <code>Foo</code> has type <code>Bar<T></code></li>
</ul>
</li>
</ul>
<p><code>Unsize</code> is used along with <a href="../ops/trait.CoerceUnsized.html"><code>ops::CoerceUnsized</code></a> to allow
"user-defined" containers such as <a href="../../std/rc/struct.Rc.html"><code>rc::Rc</code></a> to contain dynamically-sized
types. See the <a href="https://github.com/rust-lang/rfcs/blob/master/text/0982-dst-coercion.md">DST coercion RFC</a> and <a href="../../nomicon/coercions.html">the nomicon entry on coercion</a>
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