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<p class='location'>Struct BuildHasherDefault</p><div class="block items"><ul><li><a href="#implementations">Trait Implementations</a></li></ul></div><p class='location'><a href='../index.html'>std</a>::<wbr><a href='index.html'>hash</a></p><script>window.sidebarCurrent = {name: 'BuildHasherDefault', ty: 'struct', relpath: ''};</script><script defer src="sidebar-items.js"></script>
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<h1 class='fqn'><span class='in-band'>Struct <a href='../index.html'>std</a>::<wbr><a href='index.html'>hash</a>::<wbr><a class="struct" href=''>BuildHasherDefault</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>]
</a>
</span><a class='srclink' href='../../src/core/hash/mod.rs.html#459' title='goto source code'>[src]</a></span></h1>
<pre class='rust struct'>pub struct BuildHasherDefault<H>(_);</pre><div class='docblock'><p>Used to create a default <a href="trait.BuildHasher.html"><code>BuildHasher</code></a> instance for types that implement
<a href="trait.Hasher.html"><code>Hasher</code></a> and <a href="../default/trait.Default.html"><code>Default</code></a>.</p>
<p><code>BuildHasherDefault<H></code> can be used when a type <code>H</code> implements <a href="trait.Hasher.html"><code>Hasher</code></a> and
<a href="../default/trait.Default.html"><code>Default</code></a>, and you need a corresponding <a href="trait.BuildHasher.html"><code>BuildHasher</code></a> instance, but none is
defined.</p>
<p>Any <code>BuildHasherDefault</code> is <a href="https://doc.rust-lang.org/nomicon/exotic-sizes.html#zero-sized-types-zsts">zero-sized</a>. It can be created with
<a href="#method.default"><code>default</code></a>. When using <code>BuildHasherDefault</code> with <a href="../../std/collections/struct.HashMap.html"><code>HashMap</code></a> or
<a href="../../std/collections/struct.HashSet.html"><code>HashSet</code></a>, this doesn't need to be done, since they implement appropriate
<a href="../default/trait.Default.html"><code>Default</code></a> instances themselves.</p>
<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
<p>Using <code>BuildHasherDefault</code> to specify a custom <a href="trait.BuildHasher.html"><code>BuildHasher</code></a> for
<a href="../../std/collections/struct.HashMap.html"><code>HashMap</code></a>:</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">collections</span>::<span class="ident">HashMap</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">hash</span>::{<span class="ident">BuildHasherDefault</span>, <span class="ident">Hasher</span>};
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Default</span>)]</span>
<span class="kw">struct</span> <span class="ident">MyHasher</span>;
<span class="kw">impl</span> <span class="ident">Hasher</span> <span class="kw">for</span> <span class="ident">MyHasher</span> {
<span class="kw">fn</span> <span class="ident">write</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">bytes</span>: <span class="kw-2">&</span>[<span class="ident">u8</span>]) {
<span class="comment">// Your hashing algorithm goes here!</span>
<span class="macro">unimplemented</span><span class="macro">!</span>()
}
<span class="kw">fn</span> <span class="ident">finish</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">u64</span> {
<span class="comment">// Your hashing algorithm goes here!</span>
<span class="macro">unimplemented</span><span class="macro">!</span>()
}
}
<span class="kw">type</span> <span class="ident">MyBuildHasher</span> <span class="op">=</span> <span class="ident">BuildHasherDefault</span><span class="op"><</span><span class="ident">MyHasher</span><span class="op">></span>;
<span class="kw">let</span> <span class="ident">hash_map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="op"><</span><span class="ident">u32</span>, <span class="ident">u32</span>, <span class="ident">MyBuildHasher</span><span class="op">></span>::<span class="ident">default</span>();<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=fn%20main()%20%7B%0Ause%20std%3A%3Acollections%3A%3AHashMap%3B%0Ause%20std%3A%3Ahash%3A%3A%7BBuildHasherDefault%2C%20Hasher%7D%3B%0A%0A%23%5Bderive(Default)%5D%0Astruct%20MyHasher%3B%0A%0Aimpl%20Hasher%20for%20MyHasher%20%7B%0A%20%20%20%20fn%20write(%26mut%20self%2C%20bytes%3A%20%26%5Bu8%5D)%20%7B%0A%20%20%20%20%20%20%20%20%2F%2F%20Your%20hashing%20algorithm%20goes%20here!%0A%20%20%20%20%20%20%20unimplemented!()%0A%20%20%20%20%7D%0A%0A%20%20%20%20fn%20finish(%26self)%20-%3E%20u64%20%7B%0A%20%20%20%20%20%20%20%20%2F%2F%20Your%20hashing%20algorithm%20goes%20here!%0A%20%20%20%20%20%20%20%20unimplemented!()%0A%20%20%20%20%7D%0A%7D%0A%0Atype%20MyBuildHasher%20%3D%20BuildHasherDefault%3CMyHasher%3E%3B%0A%0Alet%20hash_map%20%3D%20HashMap%3A%3A%3Cu32%2C%20u32%2C%20MyBuildHasher%3E%3A%3Adefault()%3B%0A%7D">Run</a></pre>
</div><h2 id='implementations'>Trait Implementations</h2><h3 class='impl'><span class='in-band'><code>impl<H> <a class="trait" href="../../std/default/trait.Default.html" title="trait std::default::Default">Default</a> for <a class="struct" href="../../std/hash/struct.BuildHasherDefault.html" title="struct std::hash::BuildHasherDefault">BuildHasherDefault</a><H></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/core/hash/mod.rs.html#485-489' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.default' class="method"><span id='default.v' class='invisible'><code>fn <a href='../../std/default/trait.Default.html#tymethod.default' class='fnname'>default</a>() -> <a class="struct" href="../../std/hash/struct.BuildHasherDefault.html" title="struct std::hash::BuildHasherDefault">BuildHasherDefault</a><H></code></span></h4>
<div class='docblock'><p>Returns the "default value" for a type. <a href="../../std/default/trait.Default.html#tymethod.default">Read more</a></p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<H> <a class="trait" href="../../std/fmt/trait.Debug.html" title="trait std::fmt::Debug">Debug</a> for <a class="struct" href="../../std/hash/struct.BuildHasherDefault.html" title="struct std::hash::BuildHasherDefault">BuildHasherDefault</a><H></code></span><span class='out-of-band'><div class='ghost'></div><div class='since' title='Stable since Rust version 1.9.0'>1.9.0</div><a class='srclink' href='../../src/core/hash/mod.rs.html#462-466' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.fmt' class="method"><span id='fmt.v' class='invisible'><code>fn <a href='../../std/fmt/trait.Debug.html#tymethod.fmt' class='fnname'>fmt</a>(&self, f: &mut <a class="struct" href="../../std/fmt/struct.Formatter.html" title="struct std::fmt::Formatter">Formatter</a>) -> <a class="enum" href="../../std/result/enum.Result.html" title="enum std::result::Result">Result</a><<a class="primitive" href="../primitive.tuple.html">()</a>, <a class="struct" href="../../std/fmt/struct.Error.html" title="struct std::fmt::Error">Error</a>></code></span></h4>
<div class='docblock'><p>Formats the value using the given formatter.</p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<H> <a class="trait" href="../../std/clone/trait.Clone.html" title="trait std::clone::Clone">Clone</a> for <a class="struct" href="../../std/hash/struct.BuildHasherDefault.html" title="struct std::hash::BuildHasherDefault">BuildHasherDefault</a><H></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/core/hash/mod.rs.html#478-482' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.clone' class="method"><span id='clone.v' class='invisible'><code>fn <a href='../../std/clone/trait.Clone.html#tymethod.clone' class='fnname'>clone</a>(&self) -> <a class="struct" href="../../std/hash/struct.BuildHasherDefault.html" title="struct std::hash::BuildHasherDefault">BuildHasherDefault</a><H></code></span></h4>
<div class='docblock'><p>Returns a copy of the value. <a href="../../std/clone/trait.Clone.html#tymethod.clone">Read more</a></p>
</div><h4 id='method.clone_from' class="method"><span id='clone_from.v' class='invisible'><code>fn <a href='../../std/clone/trait.Clone.html#method.clone_from' class='fnname'>clone_from</a>(&mut self, source: &Self)</code><div class='since' title='Stable since Rust version 1.0.0'>1.0.0</div></span></h4>
<div class='docblock'><p>Performs copy-assignment from <code>source</code>. <a href="../../std/clone/trait.Clone.html#method.clone_from">Read more</a></p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<H> <a class="trait" href="../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a> for <a class="struct" href="../../std/hash/struct.BuildHasherDefault.html" title="struct std::hash::BuildHasherDefault">BuildHasherDefault</a><H> <span class="where fmt-newline">where<br> H: <a class="trait" href="../../std/default/trait.Default.html" title="trait std::default::Default">Default</a> + <a class="trait" href="../../std/hash/trait.Hasher.html" title="trait std::hash::Hasher">Hasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/core/hash/mod.rs.html#469-475' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='associatedtype.Hasher' class="type"><span id='Hasher.t' class='invisible'><code>type <a href='../../std/hash/trait.BuildHasher.html#associatedtype.Hasher' class="type">Hasher</a> = H</code></span></h4>
<div class='docblock'><p>Type of the hasher that will be created.</p>
</div><h4 id='method.build_hasher' class="method"><span id='build_hasher.v' class='invisible'><code>fn <a href='../../std/hash/trait.BuildHasher.html#tymethod.build_hasher' class='fnname'>build_hasher</a>(&self) -> H</code></span></h4>
<div class='docblock'><p>Creates a new hasher. <a href="../../std/hash/trait.BuildHasher.html#tymethod.build_hasher">Read more</a></p>
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