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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Returned from `Serializer::serialize_map`."><title>SerializeMap in serde::ser - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-5bc39a1768837dd0.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="serde" data-themes="" data-resource-suffix="" data-rustdoc-version="1.77.0 (aedd173a2 2024-03-17)" data-channel="1.77.0" data-search-js="search-dd67cee4cfa65049.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-4c98445ec4002617.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-48f368f3872407c8.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-04d5337699b92874.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc trait"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../serde/index.html">serde</a><span class="version">1.0.197</span></h2></div><h2 class="location"><a href="#">SerializeMap</a></h2><div class="sidebar-elems"><section><h3><a href="#required-associated-types">Required Associated Types</a></h3><ul class="block"><li><a href="#associatedtype.Error">Error</a></li><li><a href="#associatedtype.Ok">Ok</a></li></ul><h3><a href="#required-methods">Required Methods</a></h3><ul class="block"><li><a href="#tymethod.end">end</a></li><li><a href="#tymethod.serialize_key">serialize_key</a></li><li><a href="#tymethod.serialize_value">serialize_value</a></li></ul><h3><a href="#provided-methods">Provided Methods</a></h3><ul class="block"><li><a href="#method.serialize_entry">serialize_entry</a></li></ul><h3><a href="#object-safety">Object Safety</a></h3><h3><a href="#implementors">Implementors</a></h3></section><h2><a href="index.html">In serde::ser</a></h2></div></nav><div class="sidebar-resizer"></div>
<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../serde/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press S to search, ? for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Trait <a href="../index.html">serde</a>::<wbr><a href="index.html">ser</a>::<wbr><a class="trait" href="#">SerializeMap</a><button id="copy-path" title="Copy item path to clipboard"><img src="../../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../../src/serde/ser/mod.rs.html#1757-1816">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><pre class="rust item-decl"><code>pub trait SerializeMap {
type <a href="#associatedtype.Ok" class="associatedtype">Ok</a>;
type <a href="#associatedtype.Error" class="associatedtype">Error</a>: <a class="trait" href="trait.Error.html" title="trait serde::ser::Error">Error</a>;
// Required methods
fn <a href="#tymethod.serialize_key" class="fn">serialize_key</a>&lt;T&gt;(&amp;mut self, key: <a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&amp;T</a>) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;
<span class="where">where T: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.77.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span>;
<span class="item-spacer"></span> fn <a href="#tymethod.serialize_value" class="fn">serialize_value</a>&lt;T&gt;(&amp;mut self, value: <a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&amp;T</a>) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;
<span class="where">where T: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.77.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span>;
<span class="item-spacer"></span> fn <a href="#tymethod.end" class="fn">end</a>(self) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Ok" title="type serde::ser::SerializeMap::Ok">Ok</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;;
// Provided method
fn <a href="#method.serialize_entry" class="fn">serialize_entry</a>&lt;K, V&gt;(
&amp;mut self,
key: <a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&amp;K</a>,
value: <a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&amp;V</a>
) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;
<span class="where">where K: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.77.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
V: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.77.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span> { ... }
}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Returned from <code>Serializer::serialize_map</code>.</p>
<h2 id="example-use"><a class="doc-anchor" href="#example-use">§</a>Example use</h2>
<div class="example-wrap edition"><a href="#" class="tooltip" title="This example runs with edition 2021"></a><pre class="rust rust-example-rendered"><code><span class="kw">use </span>serde::ser::{Serialize, SerializeMap, Serializer};
<span class="kw">impl</span>&lt;K, V&gt; Serialize <span class="kw">for </span>HashMap&lt;K, V&gt;
<span class="kw">where
</span>K: Serialize,
V: Serialize,
{
<span class="kw">fn </span>serialize&lt;S&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, serializer: S) -&gt; <span class="prelude-ty">Result</span>&lt;S::Ok, S::Error&gt;
<span class="kw">where
</span>S: Serializer,
{
<span class="kw">let </span><span class="kw-2">mut </span>map = serializer.serialize_map(<span class="prelude-val">Some</span>(<span class="self">self</span>.len()))<span class="question-mark">?</span>;
<span class="kw">for </span>(k, v) <span class="kw">in </span><span class="self">self </span>{
map.serialize_entry(k, v)<span class="question-mark">?</span>;
}
map.end()
}
}</code></pre></div>
<h2 id="example-implementation"><a class="doc-anchor" href="#example-implementation">§</a>Example implementation</h2>
<p>The <a href="https://serde.rs/data-format.html">example data format</a> presented on the website demonstrates an
implementation of <code>SerializeMap</code> for a basic JSON data format.</p>
</div></details><h2 id="required-associated-types" class="section-header">Required Associated Types<a href="#required-associated-types" class="anchor">§</a></h2><div class="methods"><details class="toggle" open><summary><section id="associatedtype.Ok" class="method"><a class="src rightside" href="../../src/serde/ser/mod.rs.html#1759">source</a><h4 class="code-header">type <a href="#associatedtype.Ok" class="associatedtype">Ok</a></h4></section></summary><div class="docblock"><p>Must match the <code>Ok</code> type of our <code>Serializer</code>.</p>
</div></details><details class="toggle" open><summary><section id="associatedtype.Error" class="method"><a class="src rightside" href="../../src/serde/ser/mod.rs.html#1762">source</a><h4 class="code-header">type <a href="#associatedtype.Error" class="associatedtype">Error</a>: <a class="trait" href="trait.Error.html" title="trait serde::ser::Error">Error</a></h4></section></summary><div class="docblock"><p>Must match the <code>Error</code> type of our <code>Serializer</code>.</p>
</div></details></div><h2 id="required-methods" class="section-header">Required Methods<a href="#required-methods" class="anchor">§</a></h2><div class="methods"><details class="toggle method-toggle" open><summary><section id="tymethod.serialize_key" class="method"><a class="src rightside" href="../../src/serde/ser/mod.rs.html#1770-1772">source</a><h4 class="code-header">fn <a href="#tymethod.serialize_key" class="fn">serialize_key</a>&lt;T&gt;(&amp;mut self, key: <a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&amp;T</a>) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;<div class="where">where
T: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.77.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Serialize a map key.</p>
<p>If possible, <code>Serialize</code> implementations are encouraged to use
<code>serialize_entry</code> instead as it may be implemented more efficiently in
some formats compared to a pair of calls to <code>serialize_key</code> and
<code>serialize_value</code>.</p>
</div></details><details class="toggle method-toggle" open><summary><section id="tymethod.serialize_value" class="method"><a class="src rightside" href="../../src/serde/ser/mod.rs.html#1780-1782">source</a><h4 class="code-header">fn <a href="#tymethod.serialize_value" class="fn">serialize_value</a>&lt;T&gt;(&amp;mut self, value: <a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&amp;T</a>) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;<div class="where">where
T: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.77.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Serialize a map value.</p>
<h5 id="panics"><a class="doc-anchor" href="#panics">§</a>Panics</h5>
<p>Calling <code>serialize_value</code> before <code>serialize_key</code> is incorrect and is
allowed to panic or produce bogus results.</p>
</div></details><details class="toggle method-toggle" open><summary><section id="tymethod.end" class="method"><a class="src rightside" href="../../src/serde/ser/mod.rs.html#1815">source</a><h4 class="code-header">fn <a href="#tymethod.end" class="fn">end</a>(self) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Ok" title="type serde::ser::SerializeMap::Ok">Ok</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;</h4></section></summary><div class="docblock"><p>Finish serializing a map.</p>
</div></details></div><h2 id="provided-methods" class="section-header">Provided Methods<a href="#provided-methods" class="anchor">§</a></h2><div class="methods"><details class="toggle method-toggle" open><summary><section id="method.serialize_entry" class="method"><a class="src rightside" href="../../src/serde/ser/mod.rs.html#1801-1812">source</a><h4 class="code-header">fn <a href="#method.serialize_entry" class="fn">serialize_entry</a>&lt;K, V&gt;(
&amp;mut self,
key: <a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&amp;K</a>,
value: <a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&amp;V</a>
) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.77.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;<div class="where">where
K: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.77.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
V: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.77.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Serialize a map entry consisting of a key and a value.</p>
<p>Some <a href="../trait.Serialize.html"><code>Serialize</code></a> types are not able to hold a key and value in memory
at the same time so <code>SerializeMap</code> implementations are required to
support <a href="#tymethod.serialize_key"><code>serialize_key</code></a> and <a href="#tymethod.serialize_value"><code>serialize_value</code></a> individually. The
<code>serialize_entry</code> method allows serializers to optimize for the case
where key and value are both available. <a href="../trait.Serialize.html"><code>Serialize</code></a> implementations
are encouraged to use <code>serialize_entry</code> if possible.</p>
<p>The default implementation delegates to <a href="#tymethod.serialize_key"><code>serialize_key</code></a> and
<a href="#tymethod.serialize_value"><code>serialize_value</code></a>. This is appropriate for serializers that do not
care about performance or are not able to optimize <code>serialize_entry</code> any
better than this.</p>
</div></details></div><h2 id="object-safety" class="section-header">Object Safety<a href="#object-safety" class="anchor">§</a></h2><div class="object-safety-info">This trait is <b>not</b> <a href="https://doc.rust-lang.org/1.77.0/reference/items/traits.html#object-safety">object safe</a>.</div><h2 id="implementors" class="section-header">Implementors<a href="#implementors" class="anchor">§</a></h2><div id="implementors-list"><details class="toggle implementors-toggle"><summary><section id="impl-SerializeMap-for-Impossible%3COk,+Error%3E" class="impl"><a class="src rightside" href="../../src/serde/ser/impossible.rs.html#148-174">source</a><a href="#impl-SerializeMap-for-Impossible%3COk,+Error%3E" class="anchor">§</a><h3 class="code-header">impl&lt;Ok, Error&gt; <a class="trait" href="trait.SerializeMap.html" title="trait serde::ser::SerializeMap">SerializeMap</a> for <a class="struct" href="struct.Impossible.html" title="struct serde::ser::Impossible">Impossible</a>&lt;Ok, Error&gt;<div class="where">where
Error: <a class="trait" href="trait.Error.html" title="trait serde::ser::Error">Error</a>,</div></h3></section></summary><div class="impl-items"><section id="associatedtype.Ok-1" class="associatedtype trait-impl"><a href="#associatedtype.Ok-1" class="anchor">§</a><h4 class="code-header">type <a href="#associatedtype.Ok" class="associatedtype">Ok</a> = Ok</h4></section><section id="associatedtype.Error-1" class="associatedtype trait-impl"><a href="#associatedtype.Error-1" class="anchor">§</a><h4 class="code-header">type <a href="#associatedtype.Error" class="associatedtype">Error</a> = Error</h4></section></div></details></div><script src="../../trait.impl/serde/ser/trait.SerializeMap.js" async></script></section></div></main></body></html>