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<p class='location'>Trait BuildHasher</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#associated-types">Associated Types</a><div class="sidebar-links"><a href="#associatedtype.Hasher">Hasher</a></div><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.build_hasher">build_hasher</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>core</a>::<wbr><a href='index.html'>hash</a></p><script>window.sidebarCurrent = {name: 'BuildHasher', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div>
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<h1 class='fqn'><span class='in-band'>Trait <a href='../index.html'>core</a>::<wbr><a href='index.html'>hash</a>::<wbr><a class="trait" href=''>BuildHasher</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.7.0'>1.7.0</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/hash/mod.rs.html#438-461' title='goto source code'>[src]</a></span></h1>
<pre class='rust trait'>pub trait BuildHasher {
type <a href='#associatedtype.Hasher' class="type">Hasher</a>: <a class="trait" href="../../core/hash/trait.Hasher.html" title="trait core::hash::Hasher">Hasher</a>;
fn <a href='#tymethod.build_hasher' class='fnname'>build_hasher</a>(&self) -> Self::<a class="type" href="../../core/hash/trait.BuildHasher.html#associatedtype.Hasher" title="type core::hash::BuildHasher::Hasher">Hasher</a>;
}</pre><div class='docblock'><p>A trait for creating instances of <a href="trait.Hasher.html"><code>Hasher</code></a>.</p>
<p>A <code>BuildHasher</code> is typically used (e.g. by <a href="../../std/collections/struct.HashMap.html"><code>HashMap</code></a>) to create
<a href="trait.Hasher.html"><code>Hasher</code></a>s for each key such that they are hashed independently of one
another, since <a href="trait.Hasher.html"><code>Hasher</code></a>s contain state.</p>
<p>For each instance of <code>BuildHasher</code>, the <a href="trait.Hasher.html"><code>Hasher</code></a>s created by
<a href="#tymethod.build_hasher"><code>build_hasher</code></a> should be identical. That is, if the same stream of bytes
is fed into each hasher, the same output will also be generated.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">collections</span>::<span class="ident">hash_map</span>::<span class="ident">RandomState</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">hash</span>::{<span class="ident">BuildHasher</span>, <span class="ident">Hasher</span>};
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">RandomState</span>::<span class="ident">new</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">hasher_1</span> <span class="op">=</span> <span class="ident">s</span>.<span class="ident">build_hasher</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">hasher_2</span> <span class="op">=</span> <span class="ident">s</span>.<span class="ident">build_hasher</span>();
<span class="ident">hasher_1</span>.<span class="ident">write_u32</span>(<span class="number">8128</span>);
<span class="ident">hasher_2</span>.<span class="ident">write_u32</span>(<span class="number">8128</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">hasher_1</span>.<span class="ident">finish</span>(), <span class="ident">hasher_2</span>.<span class="ident">finish</span>());<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Acollections%3A%3Ahash_map%3A%3ARandomState%3B%0Ause%20std%3A%3Ahash%3A%3A%7BBuildHasher%2C%20Hasher%7D%3B%0A%0Alet%20s%20%3D%20RandomState%3A%3Anew()%3B%0Alet%20mut%20hasher_1%20%3D%20s.build_hasher()%3B%0Alet%20mut%20hasher_2%20%3D%20s.build_hasher()%3B%0A%0Ahasher_1.write_u32(8128)%3B%0Ahasher_2.write_u32(8128)%3B%0A%0Aassert_eq!(hasher_1.finish()%2C%20hasher_2.finish())%3B%0A%7D">Run</a></pre>
</div>
<h2 id='associated-types' class='small-section-header'>
Associated Types<a href='#associated-types' class='anchor'></a>
</h2>
<div class='methods'>
<h3 id='associatedtype.Hasher' class='method'><span id='Hasher.t' class='invisible'><code>type <a href='#associatedtype.Hasher' class="type">Hasher</a>: <a class="trait" href="../../core/hash/trait.Hasher.html" title="trait core::hash::Hasher">Hasher</a></code></span></h3><div class='docblock'><p>Type of the hasher that will be created.</p>
</div></div>
<h2 id='required-methods' class='small-section-header'>
Required Methods<a href='#required-methods' class='anchor'></a>
</h2>
<div class='methods'>
<h3 id='tymethod.build_hasher' class='method'><span id='build_hasher.v' class='invisible'><code>fn <a href='#tymethod.build_hasher' class='fnname'>build_hasher</a>(&self) -> Self::<a class="type" href="../../core/hash/trait.BuildHasher.html#associatedtype.Hasher" title="type core::hash::BuildHasher::Hasher">Hasher</a></code></span></h3><div class='docblock'><p>Creates a new hasher.</p>
<p>Each call to <code>build_hasher</code> on the same instance should produce identical
<a href="trait.Hasher.html"><code>Hasher</code></a>s.</p>
<h1 id="examples-1" class="section-header"><a href="#examples-1">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">collections</span>::<span class="ident">hash_map</span>::<span class="ident">RandomState</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">hash</span>::<span class="ident">BuildHasher</span>;
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">RandomState</span>::<span class="ident">new</span>();
<span class="kw">let</span> <span class="ident">new_s</span> <span class="op">=</span> <span class="ident">s</span>.<span class="ident">build_hasher</span>();<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Acollections%3A%3Ahash_map%3A%3ARandomState%3B%0Ause%20std%3A%3Ahash%3A%3ABuildHasher%3B%0A%0Alet%20s%20%3D%20RandomState%3A%3Anew()%3B%0Alet%20new_s%20%3D%20s.build_hasher()%3B%0A%7D">Run</a></pre>
</div></div>
<h2 id='implementors' class='small-section-header'>
Implementors<a href='#implementors' class='anchor'></a>
</h2>
<ul class='item-list' id='implementors-list'>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/hash/mod.rs.html#522-528' title='goto source code'>[src]</a></div><code>impl<H: <a class="trait" href="../../core/default/trait.Default.html" title="trait core::default::Default">Default</a> + <a class="trait" href="../../core/hash/trait.Hasher.html" title="trait core::hash::Hasher">Hasher</a>> BuildHasher for <a class="struct" href="../../core/hash/struct.BuildHasherDefault.html" title="struct core::hash::BuildHasherDefault">BuildHasherDefault</a><H><span class="where fmt-newline"> type <a href='#associatedtype.Hasher' class="type">Hasher</a> = H;</span></code></li>
</ul><script type="text/javascript" async
src="../../implementors/core/hash/trait.BuildHasher.js">
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