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<h1 class='fqn'><span class='in-band'>Struct <a href='../../index.html'>std</a>::<wbr><a href='../index.html'>collections</a>::<wbr><a href='index.html'>hash_map</a>::<wbr><a class="struct" href=''>HashMap</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>]
</a>
</span><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#391-398' title='goto source code'>[src]</a></span></h1>
<pre class='rust struct'>pub struct HashMap<K, V, S = <a class="struct" href="../../../std/collections/hash_map/struct.RandomState.html" title="struct std::collections::hash_map::RandomState">RandomState</a>> { /* fields omitted */ }</pre><div class='docblock'><p>A hash map implemented with linear probing and Robin Hood bucket stealing.</p>
<p>By default, <code>HashMap</code> uses a hashing algorithm selected to provide
resistance against HashDoS attacks. The algorithm is randomly seeded, and a
reasonable best-effort is made to generate this seed from a high quality,
secure source of randomness provided by the host without blocking the
program. Because of this, the randomness of the seed depends on the output
quality of the system's random number generator when the seed is created.
In particular, seeds generated when the system's entropy pool is abnormally
low such as during system boot may be of a lower quality.</p>
<p>The default hashing algorithm is currently SipHash 1-3, though this is
subject to change at any point in the future. While its performance is very
competitive for medium sized keys, other hashing algorithms will outperform
it for small keys such as integers as well as large keys such as long
strings, though those algorithms will typically <em>not</em> protect against
attacks such as HashDoS.</p>
<p>The hashing algorithm can be replaced on a per-<code>HashMap</code> basis using the
<a href="#method.default"><code>default</code></a>, <a href="#method.with_hasher"><code>with_hasher</code></a>, and <a href="#method.with_capacity_and_hasher"><code>with_capacity_and_hasher</code></a> methods. Many
alternative algorithms are available on crates.io, such as the <a href="https://crates.io/crates/fnv"><code>fnv</code></a> crate.</p>
<p>It is required that the keys implement the <a href="../../std/cmp/trait.Eq.html"><code>Eq</code></a> and <a href="../../std/hash/trait.Hash.html"><code>Hash</code></a> traits, although
this can frequently be achieved by using <code>#[derive(PartialEq, Eq, Hash)]</code>.
If you implement these yourself, it is important that the following
property holds:</p>
<pre><code class="language-text">k1 == k2 -> hash(k1) == hash(k2)
</code></pre>
<p>In other words, if two keys are equal, their hashes must be equal.</p>
<p>It is a logic error for a key to be modified in such a way that the key's
hash, as determined by the <a href="../../std/hash/trait.Hash.html"><code>Hash</code></a> trait, or its equality, as determined by
the <a href="../../std/cmp/trait.Eq.html"><code>Eq</code></a> trait, changes while it is in the map. This is normally only
possible through <a href="../../std/cell/struct.Cell.html"><code>Cell</code></a>, <a href="../../std/cell/struct.RefCell.html"><code>RefCell</code></a>, global state, I/O, or unsafe code.</p>
<p>Relevant papers/articles:</p>
<ol>
<li>Pedro Celis. <a href="https://cs.uwaterloo.ca/research/tr/1986/CS-86-14.pdf">"Robin Hood Hashing"</a></li>
<li>Emmanuel Goossaert. <a href="http://codecapsule.com/2013/11/11/robin-hood-hashing/">"Robin Hood
hashing"</a></li>
<li>Emmanuel Goossaert. <a href="http://codecapsule.com/2013/11/17/robin-hood-hashing-backward-shift-deletion/">"Robin Hood hashing: backward shift
deletion"</a></li>
</ol>
<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">HashMap</span>;
<span class="comment">// type inference lets us omit an explicit type signature (which</span>
<span class="comment">// would be `HashMap<&str, &str>` in this example).</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">book_reviews</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="comment">// review some books.</span>
<span class="ident">book_reviews</span>.<span class="ident">insert</span>(<span class="string">"Adventures of Huckleberry Finn"</span>, <span class="string">"My favorite book."</span>);
<span class="ident">book_reviews</span>.<span class="ident">insert</span>(<span class="string">"Grimms' Fairy Tales"</span>, <span class="string">"Masterpiece."</span>);
<span class="ident">book_reviews</span>.<span class="ident">insert</span>(<span class="string">"Pride and Prejudice"</span>, <span class="string">"Very enjoyable."</span>);
<span class="ident">book_reviews</span>.<span class="ident">insert</span>(<span class="string">"The Adventures of Sherlock Holmes"</span>, <span class="string">"Eye lyked it alot."</span>);
<span class="comment">// check for a specific one.</span>
<span class="kw">if</span> <span class="op">!</span><span class="ident">book_reviews</span>.<span class="ident">contains_key</span>(<span class="string">"Les Misérables"</span>) {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"We've got {} reviews, but Les Misérables ain't one."</span>,
<span class="ident">book_reviews</span>.<span class="ident">len</span>());
}
<span class="comment">// oops, this review has a lot of spelling mistakes, let's delete it.</span>
<span class="ident">book_reviews</span>.<span class="ident">remove</span>(<span class="string">"The Adventures of Sherlock Holmes"</span>);
<span class="comment">// look up the values associated with some keys.</span>
<span class="kw">let</span> <span class="ident">to_find</span> <span class="op">=</span> [<span class="string">"Pride and Prejudice"</span>, <span class="string">"Alice's Adventure in Wonderland"</span>];
<span class="kw">for</span> <span class="ident">book</span> <span class="kw">in</span> <span class="kw-2">&</span><span class="ident">to_find</span> {
<span class="kw">match</span> <span class="ident">book_reviews</span>.<span class="ident">get</span>(<span class="ident">book</span>) {
<span class="prelude-val">Some</span>(<span class="ident">review</span>) <span class="op">=></span> <span class="macro">println</span><span class="macro">!</span>(<span class="string">"{}: {}"</span>, <span class="ident">book</span>, <span class="ident">review</span>),
<span class="prelude-val">None</span> <span class="op">=></span> <span class="macro">println</span><span class="macro">!</span>(<span class="string">"{} is unreviewed."</span>, <span class="ident">book</span>)
}
}
<span class="comment">// iterate over everything.</span>
<span class="kw">for</span> (<span class="ident">book</span>, <span class="ident">review</span>) <span class="kw">in</span> <span class="kw-2">&</span><span class="ident">book_reviews</span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{}: \"{}\""</span>, <span class="ident">book</span>, <span class="ident">review</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%0A%0A%2F%2F%20type%20inference%20lets%20us%20omit%20an%20explicit%20type%20signature%20(which%0A%2F%2F%20would%20be%20%60HashMap%3C%26str%2C%20%26str%3E%60%20in%20this%20example).%0Alet%20mut%20book_reviews%20%3D%20HashMap%3A%3Anew()%3B%0A%0A%2F%2F%20review%20some%20books.%0Abook_reviews.insert(%22Adventures%20of%20Huckleberry%20Finn%22%2C%20%20%20%20%22My%20favorite%20book.%22)%3B%0Abook_reviews.insert(%22Grimms'%20Fairy%20Tales%22%2C%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%22Masterpiece.%22)%3B%0Abook_reviews.insert(%22Pride%20and%20Prejudice%22%2C%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%22Very%20enjoyable.%22)%3B%0Abook_reviews.insert(%22The%20Adventures%20of%20Sherlock%20Holmes%22%2C%20%22Eye%20lyked%20it%20alot.%22)%3B%0A%0A%2F%2F%20check%20for%20a%20specific%20one.%0Aif%20!book_reviews.contains_key(%22Les%20Mis%C3%A9rables%22)%20%7B%0A%20%20%20%20println!(%22We've%20got%20%7B%7D%20reviews%2C%20but%20Les%20Mis%C3%A9rables%20ain't%20one.%22%2C%0A%20%20%20%20%20%20%20%20%20%20%20%20%20book_reviews.len())%3B%0A%7D%0A%0A%2F%2F%20oops%2C%20this%20review%20has%20a%20lot%20of%20spelling%20mistakes%2C%20let's%20delete%20it.%0Abook_reviews.remove(%22The%20Adventures%20of%20Sherlock%20Holmes%22)%3B%0A%0A%2F%2F%20look%20up%20the%20values%20associated%20with%20some%20keys.%0Alet%20to_find%20%3D%20%5B%22Pride%20and%20Prejudice%22%2C%20%22Alice's%20Adventure%20in%20Wonderland%22%5D%3B%0Afor%20book%20in%20%26to_find%20%7B%0A%20%20%20%20match%20book_reviews.get(book)%20%7B%0A%20%20%20%20%20%20%20%20Some(review)%20%3D%3E%20println!(%22%7B%7D%3A%20%7B%7D%22%2C%20book%2C%20review)%2C%0A%20%20%20%20%20%20%20%20None%20%3D%3E%20println!(%22%7B%7D%20is%20unreviewed.%22%2C%20book)%0A%20%20%20%20%7D%0A%7D%0A%0A%2F%2F%20iterate%20over%20everything.%0Afor%20(book%2C%20review)%20in%20%26book_reviews%20%7B%0A%20%20%20%20println!(%22%7B%7D%3A%20%5C%22%7B%7D%5C%22%22%2C%20book%2C%20review)%3B%0A%7D%0A%7D">Run</a></pre>
<p><code>HashMap</code> also implements an <a href="#method.entry"><code>Entry API</code></a>, which allows
for more complex methods of getting, setting, updating and removing keys and
their values:</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="comment">// type inference lets us omit an explicit type signature (which</span>
<span class="comment">// would be `HashMap<&str, u8>` in this example).</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">player_stats</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="kw">fn</span> <span class="ident">random_stat_buff</span>() <span class="op">-></span> <span class="ident">u8</span> {
<span class="comment">// could actually return some random value here - let's just return</span>
<span class="comment">// some fixed value for now</span>
<span class="number">42</span>
}
<span class="comment">// insert a key only if it doesn't already exist</span>
<span class="ident">player_stats</span>.<span class="ident">entry</span>(<span class="string">"health"</span>).<span class="ident">or_insert</span>(<span class="number">100</span>);
<span class="comment">// insert a key using a function that provides a new value only if it</span>
<span class="comment">// doesn't already exist</span>
<span class="ident">player_stats</span>.<span class="ident">entry</span>(<span class="string">"defence"</span>).<span class="ident">or_insert_with</span>(<span class="ident">random_stat_buff</span>);
<span class="comment">// update a key, guarding against the key possibly not being set</span>
<span class="kw">let</span> <span class="ident">stat</span> <span class="op">=</span> <span class="ident">player_stats</span>.<span class="ident">entry</span>(<span class="string">"attack"</span>).<span class="ident">or_insert</span>(<span class="number">100</span>);
<span class="kw-2">*</span><span class="ident">stat</span> <span class="op">+=</span> <span class="ident">random_stat_buff</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%0A%0A%2F%2F%20type%20inference%20lets%20us%20omit%20an%20explicit%20type%20signature%20(which%0A%2F%2F%20would%20be%20%60HashMap%3C%26str%2C%20u8%3E%60%20in%20this%20example).%0Alet%20mut%20player_stats%20%3D%20HashMap%3A%3Anew()%3B%0A%0Afn%20random_stat_buff()%20-%3E%20u8%20%7B%0A%20%20%20%20%2F%2F%20could%20actually%20return%20some%20random%20value%20here%20-%20let's%20just%20return%0A%20%20%20%20%2F%2F%20some%20fixed%20value%20for%20now%0A%20%20%20%2042%0A%7D%0A%0A%2F%2F%20insert%20a%20key%20only%20if%20it%20doesn't%20already%20exist%0Aplayer_stats.entry(%22health%22).or_insert(100)%3B%0A%0A%2F%2F%20insert%20a%20key%20using%20a%20function%20that%20provides%20a%20new%20value%20only%20if%20it%0A%2F%2F%20doesn't%20already%20exist%0Aplayer_stats.entry(%22defence%22).or_insert_with(random_stat_buff)%3B%0A%0A%2F%2F%20update%20a%20key%2C%20guarding%20against%20the%20key%20possibly%20not%20being%20set%0Alet%20stat%20%3D%20player_stats.entry(%22attack%22).or_insert(100)%3B%0A*stat%20%2B%3D%20random_stat_buff()%3B%0A%7D">Run</a></pre>
<p>The easiest way to use <code>HashMap</code> with a custom type as key is to derive <a href="../../std/cmp/trait.Eq.html"><code>Eq</code></a> and <a href="../../std/hash/trait.Hash.html"><code>Hash</code></a>.
We must also derive <a href="../../std/cmp/trait.PartialEq.html"><code>PartialEq</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="attribute">#[<span class="ident">derive</span>(<span class="ident">Hash</span>, <span class="ident">Eq</span>, <span class="ident">PartialEq</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">Viking</span> {
<span class="ident">name</span>: <span class="ident">String</span>,
<span class="ident">country</span>: <span class="ident">String</span>,
}
<span class="kw">impl</span> <span class="ident">Viking</span> {
<span class="doccomment">/// Create a new Viking.</span>
<span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">name</span>: <span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">country</span>: <span class="kw-2">&</span><span class="ident">str</span>) <span class="op">-></span> <span class="ident">Viking</span> {
<span class="ident">Viking</span> { <span class="ident">name</span>: <span class="ident">name</span>.<span class="ident">to_string</span>(), <span class="ident">country</span>: <span class="ident">country</span>.<span class="ident">to_string</span>() }
}
}
<span class="comment">// Use a HashMap to store the vikings' health points.</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">vikings</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">vikings</span>.<span class="ident">insert</span>(<span class="ident">Viking</span>::<span class="ident">new</span>(<span class="string">"Einar"</span>, <span class="string">"Norway"</span>), <span class="number">25</span>);
<span class="ident">vikings</span>.<span class="ident">insert</span>(<span class="ident">Viking</span>::<span class="ident">new</span>(<span class="string">"Olaf"</span>, <span class="string">"Denmark"</span>), <span class="number">24</span>);
<span class="ident">vikings</span>.<span class="ident">insert</span>(<span class="ident">Viking</span>::<span class="ident">new</span>(<span class="string">"Harald"</span>, <span class="string">"Iceland"</span>), <span class="number">12</span>);
<span class="comment">// Use derived implementation to print the status of the vikings.</span>
<span class="kw">for</span> (<span class="ident">viking</span>, <span class="ident">health</span>) <span class="kw">in</span> <span class="kw-2">&</span><span class="ident">vikings</span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{:?} has {} hp"</span>, <span class="ident">viking</span>, <span class="ident">health</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%0A%0A%23%5Bderive(Hash%2C%20Eq%2C%20PartialEq%2C%20Debug)%5D%0Astruct%20Viking%20%7B%0A%20%20%20%20name%3A%20String%2C%0A%20%20%20%20country%3A%20String%2C%0A%7D%0A%0Aimpl%20Viking%20%7B%0A%20%20%20%20%2F%2F%2F%20Create%20a%20new%20Viking.%0A%20%20%20%20fn%20new(name%3A%20%26str%2C%20country%3A%20%26str)%20-%3E%20Viking%20%7B%0A%20%20%20%20%20%20%20%20Viking%20%7B%20name%3A%20name.to_string()%2C%20country%3A%20country.to_string()%20%7D%0A%20%20%20%20%7D%0A%7D%0A%0A%2F%2F%20Use%20a%20HashMap%20to%20store%20the%20vikings'%20health%20points.%0Alet%20mut%20vikings%20%3D%20HashMap%3A%3Anew()%3B%0A%0Avikings.insert(Viking%3A%3Anew(%22Einar%22%2C%20%22Norway%22)%2C%2025)%3B%0Avikings.insert(Viking%3A%3Anew(%22Olaf%22%2C%20%22Denmark%22)%2C%2024)%3B%0Avikings.insert(Viking%3A%3Anew(%22Harald%22%2C%20%22Iceland%22)%2C%2012)%3B%0A%0A%2F%2F%20Use%20derived%20implementation%20to%20print%20the%20status%20of%20the%20vikings.%0Afor%20(viking%2C%20health)%20in%20%26vikings%20%7B%0A%20%20%20%20println!(%22%7B%3A%3F%7D%20has%20%7B%7D%20hp%22%2C%20viking%2C%20health)%3B%0A%7D%0A%7D">Run</a></pre>
<p>A <code>HashMap</code> with fixed list of elements can be initialized from an array:</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">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">timber_resources</span>: <span class="ident">HashMap</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">i32</span><span class="op">></span> <span class="op">=</span>
[(<span class="string">"Norway"</span>, <span class="number">100</span>),
(<span class="string">"Denmark"</span>, <span class="number">50</span>),
(<span class="string">"Iceland"</span>, <span class="number">10</span>)]
.<span class="ident">iter</span>().<span class="ident">cloned</span>().<span class="ident">collect</span>();
<span class="comment">// use the values stored in map</span>
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=use%20std%3A%3Acollections%3A%3AHashMap%3B%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20timber_resources%3A%20HashMap%3C%26str%2C%20i32%3E%20%3D%0A%20%20%20%20%5B(%22Norway%22%2C%20100)%2C%0A%20%20%20%20%20(%22Denmark%22%2C%2050)%2C%0A%20%20%20%20%20(%22Iceland%22%2C%2010)%5D%0A%20%20%20%20%20.iter().cloned().collect()%3B%0A%20%20%20%20%2F%2F%20use%20the%20values%20stored%20in%20map%0A%7D%0A">Run</a></pre>
</div><h2 id='methods'>Methods</h2><h3 class='impl'><span class='in-band'><code>impl<K: <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a> + <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a>, V> <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, <a class="struct" href="../../../std/collections/hash_map/struct.RandomState.html" title="struct std::collections::hash_map::RandomState">RandomState</a>></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#588-619' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.new' class="method"><span id='new.v' class='invisible'><code>fn <a href='#method.new' class='fnname'>new</a>() -> <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, <a class="struct" href="../../../std/collections/hash_map/struct.RandomState.html" title="struct std::collections::hash_map::RandomState">RandomState</a>></code></span></h4>
<div class='docblock'><p>Creates an empty <code>HashMap</code>.</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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span>: <span class="ident">HashMap</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">isize</span><span class="op">></span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</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%0Alet%20mut%20map%3A%20HashMap%3C%26str%2C%20isize%3E%20%3D%20HashMap%3A%3Anew()%3B%0A%7D">Run</a></pre>
</div><h4 id='method.with_capacity' class="method"><span id='with_capacity.v' class='invisible'><code>fn <a href='#method.with_capacity' class='fnname'>with_capacity</a>(capacity: <a class="primitive" href="../../primitive.usize.html">usize</a>) -> <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, <a class="struct" href="../../../std/collections/hash_map/struct.RandomState.html" title="struct std::collections::hash_map::RandomState">RandomState</a>></code></span></h4>
<div class='docblock'><p>Creates an empty <code>HashMap</code> with the specified capacity.</p>
<p>The hash map will be able to hold at least <code>capacity</code> elements without
reallocating. If <code>capacity</code> is 0, the hash map will not allocate.</p>
<h1 id='examples-2' class='section-header'><a href='#examples-2'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span>: <span class="ident">HashMap</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">isize</span><span class="op">></span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">with_capacity</span>(<span class="number">10</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%0Alet%20mut%20map%3A%20HashMap%3C%26str%2C%20isize%3E%20%3D%20HashMap%3A%3Awith_capacity(10)%3B%0A%7D">Run</a></pre>
</div></div><h3 class='impl'><span class='in-band'><code>impl<K, V, S> <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#621-1275' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.with_hasher' class="method"><span id='with_hasher.v' class='invisible'><code>fn <a href='#method.with_hasher' class='fnname'>with_hasher</a>(hash_builder: S) -> <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S></code><div class='since' title='Stable since Rust version 1.7.0'>1.7.0</div></span></h4>
<div class='docblock'><p>Creates an empty <code>HashMap</code> which will use the given hash builder to hash
keys.</p>
<p>The created map has the default initial capacity.</p>
<p>Warning: <code>hash_builder</code> is normally randomly generated, and
is designed to allow HashMaps to be resistant to attacks that
cause many collisions and very poor performance. Setting it
manually using this function can expose a DoS attack vector.</p>
<h1 id='examples-3' class='section-header'><a href='#examples-3'>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">HashMap</span>;
<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">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">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">with_hasher</span>(<span class="ident">s</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="number">2</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%3Acollections%3A%3Ahash_map%3A%3ARandomState%3B%0A%0Alet%20s%20%3D%20RandomState%3A%3Anew()%3B%0Alet%20mut%20map%20%3D%20HashMap%3A%3Awith_hasher(s)%3B%0Amap.insert(1%2C%202)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.with_capacity_and_hasher' class="method"><span id='with_capacity_and_hasher.v' class='invisible'><code>fn <a href='#method.with_capacity_and_hasher' class='fnname'>with_capacity_and_hasher</a>(<br> capacity: <a class="primitive" href="../../primitive.usize.html">usize</a>, <br> hash_builder: S<br>) -> <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S></code><div class='since' title='Stable since Rust version 1.7.0'>1.7.0</div></span></h4>
<div class='docblock'><p>Creates an empty <code>HashMap</code> with the specified capacity, using <code>hash_builder</code>
to hash the keys.</p>
<p>The hash map will be able to hold at least <code>capacity</code> elements without
reallocating. If <code>capacity</code> is 0, the hash map will not allocate.</p>
<p>Warning: <code>hash_builder</code> is normally randomly generated, and
is designed to allow HashMaps to be resistant to attacks that
cause many collisions and very poor performance. Setting it
manually using this function can expose a DoS attack vector.</p>
<h1 id='examples-4' class='section-header'><a href='#examples-4'>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">HashMap</span>;
<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">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">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">with_capacity_and_hasher</span>(<span class="number">10</span>, <span class="ident">s</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="number">2</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%3Acollections%3A%3Ahash_map%3A%3ARandomState%3B%0A%0Alet%20s%20%3D%20RandomState%3A%3Anew()%3B%0Alet%20mut%20map%20%3D%20HashMap%3A%3Awith_capacity_and_hasher(10%2C%20s)%3B%0Amap.insert(1%2C%202)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.hasher' class="method"><span id='hasher.v' class='invisible'><code>fn <a href='#method.hasher' class='fnname'>hasher</a>(&self) -> &S</code><div class='since' title='Stable since Rust version 1.9.0'>1.9.0</div></span></h4>
<div class='docblock'><p>Returns a reference to the map's <a href="../../std/hash/trait.BuildHasher.html"><code>BuildHasher</code></a>.</p>
</div><h4 id='method.capacity' class="method"><span id='capacity.v' class='invisible'><code>fn <a href='#method.capacity' class='fnname'>capacity</a>(&self) -> <a class="primitive" href="../../primitive.usize.html">usize</a></code></span></h4>
<div class='docblock'><p>Returns the number of elements the map can hold without reallocating.</p>
<p>This number is a lower bound; the <code>HashMap<K, V></code> might be able to hold
more, but is guaranteed to be able to hold at least this many.</p>
<h1 id='examples-5' class='section-header'><a href='#examples-5'>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">HashMap</span>;
<span class="kw">let</span> <span class="ident">map</span>: <span class="ident">HashMap</span><span class="op"><</span><span class="ident">isize</span>, <span class="ident">isize</span><span class="op">></span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">with_capacity</span>(<span class="number">100</span>);
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">capacity</span>() <span class="op">>=</span> <span class="number">100</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%0Alet%20map%3A%20HashMap%3Cisize%2C%20isize%3E%20%3D%20HashMap%3A%3Awith_capacity(100)%3B%0Aassert!(map.capacity()%20%3E%3D%20100)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.reserve' class="method"><span id='reserve.v' class='invisible'><code>fn <a href='#method.reserve' class='fnname'>reserve</a>(&mut self, additional: <a class="primitive" href="../../primitive.usize.html">usize</a>)</code></span></h4>
<div class='docblock'><p>Reserves capacity for at least <code>additional</code> more elements to be inserted
in the <code>HashMap</code>. The collection may reserve more space to avoid
frequent reallocations.</p>
<h1 id='panics' class='section-header'><a href='#panics'>Panics</a></h1>
<p>Panics if the new allocation size overflows <a href="../../std/primitive.usize.html"><code>usize</code></a>.</p>
<h1 id='examples-6' class='section-header'><a href='#examples-6'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span>: <span class="ident">HashMap</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">isize</span><span class="op">></span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">reserve</span>(<span class="number">10</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%0Alet%20mut%20map%3A%20HashMap%3C%26str%2C%20isize%3E%20%3D%20HashMap%3A%3Anew()%3B%0Amap.reserve(10)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.shrink_to_fit' class="method"><span id='shrink_to_fit.v' class='invisible'><code>fn <a href='#method.shrink_to_fit' class='fnname'>shrink_to_fit</a>(&mut self)</code></span></h4>
<div class='docblock'><p>Shrinks the capacity of the map as much as possible. It will drop
down as much as possible while maintaining the internal rules
and possibly leaving some space in accordance with the resize policy.</p>
<h1 id='examples-7' class='section-header'><a href='#examples-7'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span>: <span class="ident">HashMap</span><span class="op"><</span><span class="ident">isize</span>, <span class="ident">isize</span><span class="op">></span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">with_capacity</span>(<span class="number">100</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="number">2</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">3</span>, <span class="number">4</span>);
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">capacity</span>() <span class="op">>=</span> <span class="number">100</span>);
<span class="ident">map</span>.<span class="ident">shrink_to_fit</span>();
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">capacity</span>() <span class="op">>=</span> <span class="number">2</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%0A%0Alet%20mut%20map%3A%20HashMap%3Cisize%2C%20isize%3E%20%3D%20HashMap%3A%3Awith_capacity(100)%3B%0Amap.insert(1%2C%202)%3B%0Amap.insert(3%2C%204)%3B%0Aassert!(map.capacity()%20%3E%3D%20100)%3B%0Amap.shrink_to_fit()%3B%0Aassert!(map.capacity()%20%3E%3D%202)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.keys' class="method"><span id='keys.v' class='invisible'><code>fn <a href='#method.keys' class='fnname'>keys</a>(&self) -> <a class="struct" href="../../../std/collections/hash_map/struct.Keys.html" title="struct std::collections::hash_map::Keys">Keys</a><K, V></code></span></h4>
<div class='docblock'><p>An iterator visiting all keys in arbitrary order.
The iterator element type is <code>&'a K</code>.</p>
<h1 id='examples-8' class='section-header'><a href='#examples-8'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"a"</span>, <span class="number">1</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"b"</span>, <span class="number">2</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"c"</span>, <span class="number">3</span>);
<span class="kw">for</span> <span class="ident">key</span> <span class="kw">in</span> <span class="ident">map</span>.<span class="ident">keys</span>() {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{}"</span>, <span class="ident">key</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(%22a%22%2C%201)%3B%0Amap.insert(%22b%22%2C%202)%3B%0Amap.insert(%22c%22%2C%203)%3B%0A%0Afor%20key%20in%20map.keys()%20%7B%0A%20%20%20%20println!(%22%7B%7D%22%2C%20key)%3B%0A%7D%0A%7D">Run</a></pre>
</div><h4 id='method.values' class="method"><span id='values.v' class='invisible'><code>fn <a href='#method.values' class='fnname'>values</a>(&self) -> <a class="struct" href="../../../std/collections/hash_map/struct.Values.html" title="struct std::collections::hash_map::Values">Values</a><K, V></code></span></h4>
<div class='docblock'><p>An iterator visiting all values in arbitrary order.
The iterator element type is <code>&'a V</code>.</p>
<h1 id='examples-9' class='section-header'><a href='#examples-9'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"a"</span>, <span class="number">1</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"b"</span>, <span class="number">2</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"c"</span>, <span class="number">3</span>);
<span class="kw">for</span> <span class="ident">val</span> <span class="kw">in</span> <span class="ident">map</span>.<span class="ident">values</span>() {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{}"</span>, <span class="ident">val</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(%22a%22%2C%201)%3B%0Amap.insert(%22b%22%2C%202)%3B%0Amap.insert(%22c%22%2C%203)%3B%0A%0Afor%20val%20in%20map.values()%20%7B%0A%20%20%20%20println!(%22%7B%7D%22%2C%20val)%3B%0A%7D%0A%7D">Run</a></pre>
</div><h4 id='method.values_mut' class="method"><span id='values_mut.v' class='invisible'><code>fn <a href='#method.values_mut' class='fnname'>values_mut</a>(&mut self) -> <a class="struct" href="../../../std/collections/hash_map/struct.ValuesMut.html" title="struct std::collections::hash_map::ValuesMut">ValuesMut</a><K, V></code><div class='since' title='Stable since Rust version 1.10.0'>1.10.0</div></span></h4>
<div class='docblock'><p>An iterator visiting all values mutably in arbitrary order.
The iterator element type is <code>&'a mut V</code>.</p>
<h1 id='examples-10' class='section-header'><a href='#examples-10'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"a"</span>, <span class="number">1</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"b"</span>, <span class="number">2</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"c"</span>, <span class="number">3</span>);
<span class="kw">for</span> <span class="ident">val</span> <span class="kw">in</span> <span class="ident">map</span>.<span class="ident">values_mut</span>() {
<span class="kw-2">*</span><span class="ident">val</span> <span class="op">=</span> <span class="kw-2">*</span><span class="ident">val</span> <span class="op">+</span> <span class="number">10</span>;
}
<span class="kw">for</span> <span class="ident">val</span> <span class="kw">in</span> <span class="ident">map</span>.<span class="ident">values</span>() {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{}"</span>, <span class="ident">val</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0A%0Amap.insert(%22a%22%2C%201)%3B%0Amap.insert(%22b%22%2C%202)%3B%0Amap.insert(%22c%22%2C%203)%3B%0A%0Afor%20val%20in%20map.values_mut()%20%7B%0A%20%20%20%20*val%20%3D%20*val%20%2B%2010%3B%0A%7D%0A%0Afor%20val%20in%20map.values()%20%7B%0A%20%20%20%20println!(%22%7B%7D%22%2C%20val)%3B%0A%7D%0A%7D">Run</a></pre>
</div><h4 id='method.iter' class="method"><span id='iter.v' class='invisible'><code>fn <a href='#method.iter' class='fnname'>iter</a>(&self) -> <a class="struct" href="../../../std/collections/hash_map/struct.Iter.html" title="struct std::collections::hash_map::Iter">Iter</a><K, V></code></span></h4>
<div class='docblock'><p>An iterator visiting all key-value pairs in arbitrary order.
The iterator element type is <code>(&'a K, &'a V)</code>.</p>
<h1 id='examples-11' class='section-header'><a href='#examples-11'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"a"</span>, <span class="number">1</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"b"</span>, <span class="number">2</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"c"</span>, <span class="number">3</span>);
<span class="kw">for</span> (<span class="ident">key</span>, <span class="ident">val</span>) <span class="kw">in</span> <span class="ident">map</span>.<span class="ident">iter</span>() {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"key: {} val: {}"</span>, <span class="ident">key</span>, <span class="ident">val</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(%22a%22%2C%201)%3B%0Amap.insert(%22b%22%2C%202)%3B%0Amap.insert(%22c%22%2C%203)%3B%0A%0Afor%20(key%2C%20val)%20in%20map.iter()%20%7B%0A%20%20%20%20println!(%22key%3A%20%7B%7D%20val%3A%20%7B%7D%22%2C%20key%2C%20val)%3B%0A%7D%0A%7D">Run</a></pre>
</div><h4 id='method.iter_mut' class="method"><span id='iter_mut.v' class='invisible'><code>fn <a href='#method.iter_mut' class='fnname'>iter_mut</a>(&mut self) -> <a class="struct" href="../../../std/collections/hash_map/struct.IterMut.html" title="struct std::collections::hash_map::IterMut">IterMut</a><K, V></code></span></h4>
<div class='docblock'><p>An iterator visiting all key-value pairs in arbitrary order,
with mutable references to the values.
The iterator element type is <code>(&'a K, &'a mut V)</code>.</p>
<h1 id='examples-12' class='section-header'><a href='#examples-12'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"a"</span>, <span class="number">1</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"b"</span>, <span class="number">2</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"c"</span>, <span class="number">3</span>);
<span class="comment">// Update all values</span>
<span class="kw">for</span> (_, <span class="ident">val</span>) <span class="kw">in</span> <span class="ident">map</span>.<span class="ident">iter_mut</span>() {
<span class="kw-2">*</span><span class="ident">val</span> <span class="op">*=</span> <span class="number">2</span>;
}
<span class="kw">for</span> (<span class="ident">key</span>, <span class="ident">val</span>) <span class="kw">in</span> <span class="kw-2">&</span><span class="ident">map</span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"key: {} val: {}"</span>, <span class="ident">key</span>, <span class="ident">val</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(%22a%22%2C%201)%3B%0Amap.insert(%22b%22%2C%202)%3B%0Amap.insert(%22c%22%2C%203)%3B%0A%0A%2F%2F%20Update%20all%20values%0Afor%20(_%2C%20val)%20in%20map.iter_mut()%20%7B%0A%20%20%20%20*val%20*%3D%202%3B%0A%7D%0A%0Afor%20(key%2C%20val)%20in%20%26map%20%7B%0A%20%20%20%20println!(%22key%3A%20%7B%7D%20val%3A%20%7B%7D%22%2C%20key%2C%20val)%3B%0A%7D%0A%7D">Run</a></pre>
</div><h4 id='method.entry' class="method"><span id='entry.v' class='invisible'><code>fn <a href='#method.entry' class='fnname'>entry</a>(&mut self, key: K) -> <a class="enum" href="../../../std/collections/hash_map/enum.Entry.html" title="enum std::collections::hash_map::Entry">Entry</a><K, V></code></span></h4>
<div class='docblock'><p>Gets the given key's corresponding entry in the map for in-place manipulation.</p>
<h1 id='examples-13' class='section-header'><a href='#examples-13'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">letters</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="kw">for</span> <span class="ident">ch</span> <span class="kw">in</span> <span class="string">"a short treatise on fungi"</span>.<span class="ident">chars</span>() {
<span class="kw">let</span> <span class="ident">counter</span> <span class="op">=</span> <span class="ident">letters</span>.<span class="ident">entry</span>(<span class="ident">ch</span>).<span class="ident">or_insert</span>(<span class="number">0</span>);
<span class="kw-2">*</span><span class="ident">counter</span> <span class="op">+=</span> <span class="number">1</span>;
}
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">letters</span>[<span class="kw-2">&</span><span class="string">'s'</span>], <span class="number">2</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">letters</span>[<span class="kw-2">&</span><span class="string">'t'</span>], <span class="number">3</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">letters</span>[<span class="kw-2">&</span><span class="string">'u'</span>], <span class="number">1</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">letters</span>.<span class="ident">get</span>(<span class="kw-2">&</span><span class="string">'y'</span>), <span class="prelude-val">None</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%0A%0Alet%20mut%20letters%20%3D%20HashMap%3A%3Anew()%3B%0A%0Afor%20ch%20in%20%22a%20short%20treatise%20on%20fungi%22.chars()%20%7B%0A%20%20%20%20let%20counter%20%3D%20letters.entry(ch).or_insert(0)%3B%0A%20%20%20%20*counter%20%2B%3D%201%3B%0A%7D%0A%0Aassert_eq!(letters%5B%26's'%5D%2C%202)%3B%0Aassert_eq!(letters%5B%26't'%5D%2C%203)%3B%0Aassert_eq!(letters%5B%26'u'%5D%2C%201)%3B%0Aassert_eq!(letters.get(%26'y')%2C%20None)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.len' class="method"><span id='len.v' class='invisible'><code>fn <a href='#method.len' class='fnname'>len</a>(&self) -> <a class="primitive" href="../../primitive.usize.html">usize</a></code></span></h4>
<div class='docblock'><p>Returns the number of elements in the map.</p>
<h1 id='examples-14' class='section-header'><a href='#examples-14'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">len</span>(), <span class="number">0</span>);
<span class="ident">a</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="string">"a"</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">len</span>(), <span class="number">1</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%0A%0Alet%20mut%20a%20%3D%20HashMap%3A%3Anew()%3B%0Aassert_eq!(a.len()%2C%200)%3B%0Aa.insert(1%2C%20%22a%22)%3B%0Aassert_eq!(a.len()%2C%201)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.is_empty' class="method"><span id='is_empty.v' class='invisible'><code>fn <a href='#method.is_empty' class='fnname'>is_empty</a>(&self) -> <a class="primitive" href="../../primitive.bool.html">bool</a></code></span></h4>
<div class='docblock'><p>Returns true if the map contains no elements.</p>
<h1 id='examples-15' class='section-header'><a href='#examples-15'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">is_empty</span>());
<span class="ident">a</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="string">"a"</span>);
<span class="macro">assert</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">a</span>.<span class="ident">is_empty</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%0A%0Alet%20mut%20a%20%3D%20HashMap%3A%3Anew()%3B%0Aassert!(a.is_empty())%3B%0Aa.insert(1%2C%20%22a%22)%3B%0Aassert!(!a.is_empty())%3B%0A%7D">Run</a></pre>
</div><h4 id='method.drain' class="method"><span id='drain.v' class='invisible'><code>fn <a href='#method.drain' class='fnname'>drain</a>(&mut self) -> <a class="struct" href="../../../std/collections/hash_map/struct.Drain.html" title="struct std::collections::hash_map::Drain">Drain</a><K, V></code><div class='since' title='Stable since Rust version 1.6.0'>1.6.0</div></span></h4>
<div class='docblock'><p>Clears the map, returning all key-value pairs as an iterator. Keeps the
allocated memory for reuse.</p>
<h1 id='examples-16' class='section-header'><a href='#examples-16'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">a</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="string">"a"</span>);
<span class="ident">a</span>.<span class="ident">insert</span>(<span class="number">2</span>, <span class="string">"b"</span>);
<span class="kw">for</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="kw">in</span> <span class="ident">a</span>.<span class="ident">drain</span>().<span class="ident">take</span>(<span class="number">1</span>) {
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">k</span> <span class="op">==</span> <span class="number">1</span> <span class="op">||</span> <span class="ident">k</span> <span class="op">==</span> <span class="number">2</span>);
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">v</span> <span class="op">==</span> <span class="string">"a"</span> <span class="op">||</span> <span class="ident">v</span> <span class="op">==</span> <span class="string">"b"</span>);
}
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">is_empty</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%0A%0Alet%20mut%20a%20%3D%20HashMap%3A%3Anew()%3B%0Aa.insert(1%2C%20%22a%22)%3B%0Aa.insert(2%2C%20%22b%22)%3B%0A%0Afor%20(k%2C%20v)%20in%20a.drain().take(1)%20%7B%0A%20%20%20%20assert!(k%20%3D%3D%201%20%7C%7C%20k%20%3D%3D%202)%3B%0A%20%20%20%20assert!(v%20%3D%3D%20%22a%22%20%7C%7C%20v%20%3D%3D%20%22b%22)%3B%0A%7D%0A%0Aassert!(a.is_empty())%3B%0A%7D">Run</a></pre>
</div><h4 id='method.clear' class="method"><span id='clear.v' class='invisible'><code>fn <a href='#method.clear' class='fnname'>clear</a>(&mut self)</code></span></h4>
<div class='docblock'><p>Clears the map, removing all key-value pairs. Keeps the allocated memory
for reuse.</p>
<h1 id='examples-17' class='section-header'><a href='#examples-17'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">a</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="string">"a"</span>);
<span class="ident">a</span>.<span class="ident">clear</span>();
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">is_empty</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%0A%0Alet%20mut%20a%20%3D%20HashMap%3A%3Anew()%3B%0Aa.insert(1%2C%20%22a%22)%3B%0Aa.clear()%3B%0Aassert!(a.is_empty())%3B%0A%7D">Run</a></pre>
</div><h4 id='method.get' class="method"><span id='get.v' class='invisible'><code>fn <a href='#method.get' class='fnname'>get</a><Q: ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>>(&self, k: &Q) -> <a class="enum" href="../../../std/option/enum.Option.html" title="enum std::option::Option">Option</a><&V> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/borrow/trait.Borrow.html" title="trait std::borrow::Borrow">Borrow</a><Q>,<br> Q: <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a> + <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a>, </span></code></span></h4>
<div class='docblock'><p>Returns a reference to the value corresponding to the key.</p>
<p>The key may be any borrowed form of the map's key type, but
<a href="../../std/hash/trait.Hash.html"><code>Hash</code></a> and <a href="../../std/cmp/trait.Eq.html"><code>Eq</code></a> on the borrowed form <em>must</em> match those for
the key type.</p>
<h1 id='examples-18' class='section-header'><a href='#examples-18'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="string">"a"</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">get</span>(<span class="kw-2">&</span><span class="number">1</span>), <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="string">"a"</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">get</span>(<span class="kw-2">&</span><span class="number">2</span>), <span class="prelude-val">None</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(1%2C%20%22a%22)%3B%0Aassert_eq!(map.get(%261)%2C%20Some(%26%22a%22))%3B%0Aassert_eq!(map.get(%262)%2C%20None)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.contains_key' class="method"><span id='contains_key.v' class='invisible'><code>fn <a href='#method.contains_key' class='fnname'>contains_key</a><Q: ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>>(&self, k: &Q) -> <a class="primitive" href="../../primitive.bool.html">bool</a> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/borrow/trait.Borrow.html" title="trait std::borrow::Borrow">Borrow</a><Q>,<br> Q: <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a> + <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a>, </span></code></span></h4>
<div class='docblock'><p>Returns true if the map contains a value for the specified key.</p>
<p>The key may be any borrowed form of the map's key type, but
<a href="../../std/hash/trait.Hash.html"><code>Hash</code></a> and <a href="../../std/cmp/trait.Eq.html"><code>Eq</code></a> on the borrowed form <em>must</em> match those for
the key type.</p>
<h1 id='examples-19' class='section-header'><a href='#examples-19'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="string">"a"</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">contains_key</span>(<span class="kw-2">&</span><span class="number">1</span>), <span class="bool-val">true</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">contains_key</span>(<span class="kw-2">&</span><span class="number">2</span>), <span class="bool-val">false</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(1%2C%20%22a%22)%3B%0Aassert_eq!(map.contains_key(%261)%2C%20true)%3B%0Aassert_eq!(map.contains_key(%262)%2C%20false)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.get_mut' class="method"><span id='get_mut.v' class='invisible'><code>fn <a href='#method.get_mut' class='fnname'>get_mut</a><Q: ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>>(&mut self, k: &Q) -> <a class="enum" href="../../../std/option/enum.Option.html" title="enum std::option::Option">Option</a><&mut V> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/borrow/trait.Borrow.html" title="trait std::borrow::Borrow">Borrow</a><Q>,<br> Q: <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a> + <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a>, </span></code></span></h4>
<div class='docblock'><p>Returns a mutable reference to the value corresponding to the key.</p>
<p>The key may be any borrowed form of the map's key type, but
<a href="../../std/hash/trait.Hash.html"><code>Hash</code></a> and <a href="../../std/cmp/trait.Eq.html"><code>Eq</code></a> on the borrowed form <em>must</em> match those for
the key type.</p>
<h1 id='examples-20' class='section-header'><a href='#examples-20'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="string">"a"</span>);
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">x</span>) <span class="op">=</span> <span class="ident">map</span>.<span class="ident">get_mut</span>(<span class="kw-2">&</span><span class="number">1</span>) {
<span class="kw-2">*</span><span class="ident">x</span> <span class="op">=</span> <span class="string">"b"</span>;
}
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>[<span class="kw-2">&</span><span class="number">1</span>], <span class="string">"b"</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(1%2C%20%22a%22)%3B%0Aif%20let%20Some(x)%20%3D%20map.get_mut(%261)%20%7B%0A%20%20%20%20*x%20%3D%20%22b%22%3B%0A%7D%0Aassert_eq!(map%5B%261%5D%2C%20%22b%22)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.insert' class="method"><span id='insert.v' class='invisible'><code>fn <a href='#method.insert' class='fnname'>insert</a>(&mut self, k: K, v: V) -> <a class="enum" href="../../../std/option/enum.Option.html" title="enum std::option::Option">Option</a><V></code></span></h4>
<div class='docblock'><p>Inserts a key-value pair into the map.</p>
<p>If the map did not have this key present, <a href="../../std/option/enum.Option.html#variant.None"><code>None</code></a> is returned.</p>
<p>If the map did have this key present, the value is updated, and the old
value is returned. The key is not updated, though; this matters for
types that can be <code>==</code> without being identical. See the <a href="index.html#insert-and-complex-keys">module-level
documentation</a> for more.</p>
<h1 id='examples-21' class='section-header'><a href='#examples-21'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">37</span>, <span class="string">"a"</span>), <span class="prelude-val">None</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">is_empty</span>(), <span class="bool-val">false</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">37</span>, <span class="string">"b"</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">37</span>, <span class="string">"c"</span>), <span class="prelude-val">Some</span>(<span class="string">"b"</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>[<span class="kw-2">&</span><span class="number">37</span>], <span class="string">"c"</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Aassert_eq!(map.insert(37%2C%20%22a%22)%2C%20None)%3B%0Aassert_eq!(map.is_empty()%2C%20false)%3B%0A%0Amap.insert(37%2C%20%22b%22)%3B%0Aassert_eq!(map.insert(37%2C%20%22c%22)%2C%20Some(%22b%22))%3B%0Aassert_eq!(map%5B%2637%5D%2C%20%22c%22)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.remove' class="method"><span id='remove.v' class='invisible'><code>fn <a href='#method.remove' class='fnname'>remove</a><Q: ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>>(&mut self, k: &Q) -> <a class="enum" href="../../../std/option/enum.Option.html" title="enum std::option::Option">Option</a><V> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/borrow/trait.Borrow.html" title="trait std::borrow::Borrow">Borrow</a><Q>,<br> Q: <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a> + <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a>, </span></code></span></h4>
<div class='docblock'><p>Removes a key from the map, returning the value at the key if the key
was previously in the map.</p>
<p>The key may be any borrowed form of the map's key type, but
<a href="../../std/hash/trait.Hash.html"><code>Hash</code></a> and <a href="../../std/cmp/trait.Eq.html"><code>Eq</code></a> on the borrowed form <em>must</em> match those for
the key type.</p>
<h1 id='examples-22' class='section-header'><a href='#examples-22'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="number">1</span>, <span class="string">"a"</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">remove</span>(<span class="kw-2">&</span><span class="number">1</span>), <span class="prelude-val">Some</span>(<span class="string">"a"</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">remove</span>(<span class="kw-2">&</span><span class="number">1</span>), <span class="prelude-val">None</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(1%2C%20%22a%22)%3B%0Aassert_eq!(map.remove(%261)%2C%20Some(%22a%22))%3B%0Aassert_eq!(map.remove(%261)%2C%20None)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.retain' class="method"><span id='retain.v' class='invisible'><code>fn <a href='#method.retain' class='fnname'>retain</a><F>(&mut self, f: F) <span class="where fmt-newline">where<br> F: <a class="trait" href="../../../std/ops/trait.FnMut.html" title="trait std::ops::FnMut">FnMut</a>(&K, &mut V) -> <a class="primitive" href="../../primitive.bool.html">bool</a>, </span></code><div class='since' title='Stable since Rust version 1.18.0'>1.18.0</div></span></h4>
<div class='docblock'><p>Retains only the elements specified by the predicate.</p>
<p>In other words, remove all pairs <code>(k, v)</code> such that <code>f(&k,&mut v)</code> returns <code>false</code>.</p>
<h1 id='examples-23' class='section-header'><a href='#examples-23'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span>: <span class="ident">HashMap</span><span class="op"><</span><span class="ident">isize</span>, <span class="ident">isize</span><span class="op">></span> <span class="op">=</span> (<span class="number">0</span>..<span class="number">8</span>).<span class="ident">map</span>(<span class="op">|</span><span class="ident">x</span><span class="op">|</span>(<span class="ident">x</span>, <span class="ident">x</span><span class="kw-2">*</span><span class="number">10</span>)).<span class="ident">collect</span>();
<span class="ident">map</span>.<span class="ident">retain</span>(<span class="op">|</span><span class="kw-2">&</span><span class="ident">k</span>, _<span class="op">|</span> <span class="ident">k</span> <span class="op">%</span> <span class="number">2</span> <span class="op">==</span> <span class="number">0</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">len</span>(), <span class="number">4</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%0A%0Alet%20mut%20map%3A%20HashMap%3Cisize%2C%20isize%3E%20%3D%20(0..8).map(%7Cx%7C(x%2C%20x*10)).collect()%3B%0Amap.retain(%7C%26k%2C%20_%7C%20k%20%25%202%20%3D%3D%200)%3B%0Aassert_eq!(map.len()%2C%204)%3B%0A%7D">Run</a></pre>
</div></div><h2 id='implementations'>Trait Implementations</h2><h3 class='impl'><span class='in-band'><code>impl<K: <a class="trait" href="../../../std/clone/trait.Clone.html" title="trait std::clone::Clone">Clone</a>, V: <a class="trait" href="../../../std/clone/trait.Clone.html" title="trait std::clone::Clone">Clone</a>, S: <a class="trait" href="../../../std/clone/trait.Clone.html" title="trait std::clone::Clone">Clone</a>> <a class="trait" href="../../../std/clone/trait.Clone.html" title="trait std::clone::Clone">Clone</a> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#389' 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/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S></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></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<K, V, S> <a class="trait" href="../../../std/cmp/trait.PartialEq.html" title="trait std::cmp::PartialEq">PartialEq</a> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> V: <a class="trait" href="../../../std/cmp/trait.PartialEq.html" title="trait std::cmp::PartialEq">PartialEq</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#1278-1290' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.eq' class="method"><span id='eq.v' class='invisible'><code>fn <a href='../../../std/cmp/trait.PartialEq.html#tymethod.eq' class='fnname'>eq</a>(&self, other: &<a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S>) -> <a class="primitive" href="../../primitive.bool.html">bool</a></code></span></h4>
<div class='docblock'><p>This method tests for <code>self</code> and <code>other</code> values to be equal, and is used by <code>==</code>. <a href="../../../std/cmp/trait.PartialEq.html#tymethod.eq">Read more</a></p>
</div><h4 id='method.ne' class="method"><span id='ne.v' class='invisible'><code>fn <a href='../../../std/cmp/trait.PartialEq.html#method.ne' class='fnname'>ne</a>(&self, other: &Rhs) -> <a class="primitive" href="../../primitive.bool.html">bool</a></code></span></h4>
<div class='docblock'><p>This method tests for <code>!=</code>.</p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<K, V, S> <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> V: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#1293-1298' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'></div><h3 class='impl'><span class='in-band'><code>impl<K, V, S> <a class="trait" href="../../../std/fmt/trait.Debug.html" title="trait std::fmt::Debug">Debug</a> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a> + <a class="trait" href="../../../std/fmt/trait.Debug.html" title="trait std::fmt::Debug">Debug</a>,<br> V: <a class="trait" href="../../../std/fmt/trait.Debug.html" title="trait std::fmt::Debug">Debug</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#1301-1309' 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="type" href="../../../std/fmt/type.Result.html" title="type std::fmt::Result">Result</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<K, V, S> <a class="trait" href="../../../std/default/trait.Default.html" title="trait std::default::Default">Default</a> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a> + <a class="trait" href="../../../std/default/trait.Default.html" title="trait std::default::Default">Default</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#1312-1320' 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/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S></code></span></h4>
<div class='docblock'><p>Creates an empty <code>HashMap<K, V, S></code>, with the <code>Default</code> value for the hasher.</p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<'a, K, Q: ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, V, S> <a class="trait" href="../../../std/ops/trait.Index.html" title="trait std::ops::Index">Index</a><&'a Q> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a> + <a class="trait" href="../../../std/borrow/trait.Borrow.html" title="trait std::borrow::Borrow">Borrow</a><Q>,<br> Q: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#1323-1334' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='associatedtype.Output' class="type"><span id='Output.t' class='invisible'><code>type <a href='../../../std/ops/trait.Index.html#associatedtype.Output' class="type">Output</a> = V</code></span></h4>
<div class='docblock'><p>The returned type after indexing</p>
</div><h4 id='method.index' class="method"><span id='index.v' class='invisible'><code>fn <a href='../../../std/ops/trait.Index.html#tymethod.index' class='fnname'>index</a>(&self, index: &Q) -> &V</code></span></h4>
<div class='docblock'><p>The method for the indexing (<code>container[index]</code>) operation</p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<'a, K, V, S> <a class="trait" href="../../../std/iter/trait.IntoIterator.html" title="trait std::iter::IntoIterator">IntoIterator</a> for &'a <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#1599-1609' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='associatedtype.Item' class="type"><span id='Item.t' class='invisible'><code>type <a href='../../../std/iter/trait.IntoIterator.html#associatedtype.Item' class="type">Item</a> = <a class="primitive" href="../../primitive.tuple.html">(</a>&'a K, &'a V<a class="primitive" href="../../primitive.tuple.html">)</a></code></span></h4>
<div class='docblock'><p>The type of the elements being iterated over.</p>
</div><h4 id='associatedtype.IntoIter' class="type"><span id='IntoIter.t' class='invisible'><code>type <a href='../../../std/iter/trait.IntoIterator.html#associatedtype.IntoIter' class="type">IntoIter</a> = <a class="struct" href="../../../std/collections/hash_map/struct.Iter.html" title="struct std::collections::hash_map::Iter">Iter</a><'a, K, V></code></span></h4>
<div class='docblock'><p>Which kind of iterator are we turning this into?</p>
</div><h4 id='method.into_iter' class="method"><span id='into_iter.v' class='invisible'><code>fn <a href='../../../std/iter/trait.IntoIterator.html#tymethod.into_iter' class='fnname'>into_iter</a>(self) -> <a class="struct" href="../../../std/collections/hash_map/struct.Iter.html" title="struct std::collections::hash_map::Iter">Iter</a><'a, K, V></code></span></h4>
<div class='docblock'><p>Creates an iterator from a value. <a href="../../../std/iter/trait.IntoIterator.html#tymethod.into_iter">Read more</a></p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<'a, K, V, S> <a class="trait" href="../../../std/iter/trait.IntoIterator.html" title="trait std::iter::IntoIterator">IntoIterator</a> for &'a mut <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#1612-1622' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='associatedtype.Item-1' class="type"><span id='Item.t-1' class='invisible'><code>type <a href='../../../std/iter/trait.IntoIterator.html#associatedtype.Item' class="type">Item</a> = <a class="primitive" href="../../primitive.tuple.html">(</a>&'a K, &'a mut V<a class="primitive" href="../../primitive.tuple.html">)</a></code></span></h4>
<div class='docblock'><p>The type of the elements being iterated over.</p>
</div><h4 id='associatedtype.IntoIter-1' class="type"><span id='IntoIter.t-1' class='invisible'><code>type <a href='../../../std/iter/trait.IntoIterator.html#associatedtype.IntoIter' class="type">IntoIter</a> = <a class="struct" href="../../../std/collections/hash_map/struct.IterMut.html" title="struct std::collections::hash_map::IterMut">IterMut</a><'a, K, V></code></span></h4>
<div class='docblock'><p>Which kind of iterator are we turning this into?</p>
</div><h4 id='method.into_iter-1' class="method"><span id='into_iter.v-1' class='invisible'><code>fn <a href='../../../std/iter/trait.IntoIterator.html#tymethod.into_iter' class='fnname'>into_iter</a>(self) -> <a class="struct" href="../../../std/collections/hash_map/struct.IterMut.html" title="struct std::collections::hash_map::IterMut">IterMut</a><'a, K, V></code></span></h4>
<div class='docblock'><p>Creates an iterator from a value. <a href="../../../std/iter/trait.IntoIterator.html#tymethod.into_iter">Read more</a></p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<K, V, S> <a class="trait" href="../../../std/iter/trait.IntoIterator.html" title="trait std::iter::IntoIterator">IntoIterator</a> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#1625-1652' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='associatedtype.Item-2' class="type"><span id='Item.t-2' class='invisible'><code>type <a href='../../../std/iter/trait.IntoIterator.html#associatedtype.Item' class="type">Item</a> = <a class="primitive" href="../../primitive.tuple.html">(</a>K, V<a class="primitive" href="../../primitive.tuple.html">)</a></code></span></h4>
<div class='docblock'><p>The type of the elements being iterated over.</p>
</div><h4 id='associatedtype.IntoIter-2' class="type"><span id='IntoIter.t-2' class='invisible'><code>type <a href='../../../std/iter/trait.IntoIterator.html#associatedtype.IntoIter' class="type">IntoIter</a> = <a class="struct" href="../../../std/collections/hash_map/struct.IntoIter.html" title="struct std::collections::hash_map::IntoIter">IntoIter</a><K, V></code></span></h4>
<div class='docblock'><p>Which kind of iterator are we turning this into?</p>
</div><h4 id='method.into_iter-2' class="method"><span id='into_iter.v-2' class='invisible'><code>fn <a href='../../../std/iter/trait.IntoIterator.html#tymethod.into_iter' class='fnname'>into_iter</a>(self) -> <a class="struct" href="../../../std/collections/hash_map/struct.IntoIter.html" title="struct std::collections::hash_map::IntoIter">IntoIter</a><K, V></code></span></h4>
<div class='docblock'><p>Creates a consuming iterator, that is, one that moves each key-value
pair out of the map in arbitrary order. The map cannot be used after
calling this.</p>
<h1 id='examples-24' class='section-header'><a href='#examples-24'>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">HashMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">HashMap</span>::<span class="ident">new</span>();
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"a"</span>, <span class="number">1</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"b"</span>, <span class="number">2</span>);
<span class="ident">map</span>.<span class="ident">insert</span>(<span class="string">"c"</span>, <span class="number">3</span>);
<span class="comment">// Not possible with .iter()</span>
<span class="kw">let</span> <span class="ident">vec</span>: <span class="ident">Vec</span><span class="op"><</span>(<span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">isize</span>)<span class="op">></span> <span class="op">=</span> <span class="ident">map</span>.<span class="ident">into_iter</span>().<span class="ident">collect</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%0A%0Alet%20mut%20map%20%3D%20HashMap%3A%3Anew()%3B%0Amap.insert(%22a%22%2C%201)%3B%0Amap.insert(%22b%22%2C%202)%3B%0Amap.insert(%22c%22%2C%203)%3B%0A%0A%2F%2F%20Not%20possible%20with%20.iter()%0Alet%20vec%3A%20Vec%3C(%26str%2C%20isize)%3E%20%3D%20map.into_iter().collect()%3B%0A%7D">Run</a></pre>
</div></div><h3 class='impl'><span class='in-band'><code>impl<K, V, S> <a class="trait" href="../../../std/iter/trait.FromIterator.html" title="trait std::iter::FromIterator">FromIterator</a><<a class="primitive" href="../../primitive.tuple.html">(</a>K, V<a class="primitive" href="../../primitive.tuple.html">)</a>> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a> + <a class="trait" href="../../../std/default/trait.Default.html" title="trait std::default::Default">Default</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#2257-2266' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.from_iter' class="method"><span id='from_iter.v' class='invisible'><code>fn <a href='../../../std/iter/trait.FromIterator.html#tymethod.from_iter' class='fnname'>from_iter</a><T: <a class="trait" href="../../../std/iter/trait.IntoIterator.html" title="trait std::iter::IntoIterator">IntoIterator</a><Item = <a class="primitive" href="../../primitive.tuple.html">(</a>K, V<a class="primitive" href="../../primitive.tuple.html">)</a>>>(iter: T) -> <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S></code></span></h4>
<div class='docblock'><p>Creates a value from an iterator. <a href="../../../std/iter/trait.FromIterator.html#tymethod.from_iter">Read more</a></p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<K, V, S> <a class="trait" href="../../../std/iter/trait.Extend.html" title="trait std::iter::Extend">Extend</a><<a class="primitive" href="../../primitive.tuple.html">(</a>K, V<a class="primitive" href="../../primitive.tuple.html">)</a>> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#2269-2289' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.extend' class="method"><span id='extend.v' class='invisible'><code>fn <a href='../../../std/iter/trait.Extend.html#tymethod.extend' class='fnname'>extend</a><T: <a class="trait" href="../../../std/iter/trait.IntoIterator.html" title="trait std::iter::IntoIterator">IntoIterator</a><Item = <a class="primitive" href="../../primitive.tuple.html">(</a>K, V<a class="primitive" href="../../primitive.tuple.html">)</a>>>(&mut self, iter: T)</code></span></h4>
<div class='docblock'><p>Extends a collection with the contents of an iterator. <a href="../../../std/iter/trait.Extend.html#tymethod.extend">Read more</a></p>
</div></div><h3 class='impl'><span class='in-band'><code>impl<'a, K, V, S> <a class="trait" href="../../../std/iter/trait.Extend.html" title="trait std::iter::Extend">Extend</a><<a class="primitive" href="../../primitive.tuple.html">(</a>&'a K, &'a V<a class="primitive" href="../../primitive.tuple.html">)</a>> for <a class="struct" href="../../../std/collections/struct.HashMap.html" title="struct std::collections::HashMap">HashMap</a><K, V, S> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Eq.html" title="trait std::cmp::Eq">Eq</a> + <a class="trait" href="../../../std/hash/trait.Hash.html" title="trait std::hash::Hash">Hash</a> + <a class="trait" href="../../../std/marker/trait.Copy.html" title="trait std::marker::Copy">Copy</a>,<br> V: <a class="trait" href="../../../std/marker/trait.Copy.html" title="trait std::marker::Copy">Copy</a>,<br> S: <a class="trait" href="../../../std/hash/trait.BuildHasher.html" title="trait std::hash::BuildHasher">BuildHasher</a>, </span></code></span><span class='out-of-band'><div class='ghost'></div><div class='since' title='Stable since Rust version 1.4.0'>1.4.0</div><a class='srclink' href='../../../src/std/collections/hash/map.rs.html#2292-2300' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.extend-1' class="method"><span id='extend.v-1' class='invisible'><code>fn <a href='../../../std/iter/trait.Extend.html#tymethod.extend' class='fnname'>extend</a><T: <a class="trait" href="../../../std/iter/trait.IntoIterator.html" title="trait std::iter::IntoIterator">IntoIterator</a><Item = <a class="primitive" href="../../primitive.tuple.html">(</a>&'a K, &'a V<a class="primitive" href="../../primitive.tuple.html">)</a>>>(&mut self, iter: T)</code></span></h4>
<div class='docblock'><p>Extends a collection with the contents of an iterator. <a href="../../../std/iter/trait.Extend.html#tymethod.extend">Read more</a></p>
</div></div></section>
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