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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`."><meta name="keywords" content="rust, rustlang, rust-lang, SerializeMap"><title>SerializeMap in serde::ser - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../../dark.css" disabled><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.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">&#9776;</button><a class="sidebar-logo" href="../../serde/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2 class="location"></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../serde/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">SerializeMap</a></h2><div class="sidebar-elems"><section><div class="block"><h3 class="sidebar-title"><a href="#required-associated-types">Required Associated Types</a></h3><ul><li><a href="#associatedtype.Error">Error</a></li><li><a href="#associatedtype.Ok">Ok</a></li></ul></div><div class="block"><h3 class="sidebar-title"><a href="#required-methods">Required Methods</a></h3><ul><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></div><div class="block"><h3 class="sidebar-title"><a href="#provided-methods">Provided Methods</a></h3><ul><li><a href="#method.serialize_entry">serialize_entry</a></li></ul></div><div class="block"><h3 class="sidebar-title"><a href="#implementors">Implementors</a></h3></div></section><h2 class="location"><a href="index.html">In serde::ser</a></h2></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../../serde/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press S to search, ? for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><button type="button">?</button></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav></div><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn"><span class="in-band">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" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span></h1><span class="out-of-band"><a class="srclink" href="../../src/serde/ser/mod.rs.html#1793-1852">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">&#x2212;</span>]</a></span></div><div class="docblock item-decl"><pre class="rust trait"><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>;
fn <a href="#tymethod.serialize_key" class="fnname">serialize_key</a>&lt;T:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/1.64.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(&amp;mut self, key: <a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.reference.html">&amp;</a>T) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.64.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;<br>&nbsp;&nbsp;&nbsp; <span class="where">where<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;T: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a></span>;
<span class="item-spacer"></span> fn <a href="#tymethod.serialize_value" class="fnname">serialize_value</a>&lt;T:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/1.64.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&amp;mut self,<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;value: <a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.reference.html">&amp;</a>T<br>&nbsp;&nbsp;&nbsp;&nbsp;) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.64.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;<br>&nbsp;&nbsp;&nbsp; <span class="where">where<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;T: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a></span>;
<span class="item-spacer"></span> fn <a href="#tymethod.end" class="fnname">end</a>(self) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.64.0/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;;
fn <a href="#method.serialize_entry" class="fnname">serialize_entry</a>&lt;K:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/1.64.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, V:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/1.64.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&amp;mut self,<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;key: <a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.reference.html">&amp;</a>K,<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;value: <a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.reference.html">&amp;</a>V<br>&nbsp;&nbsp;&nbsp;&nbsp;) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.64.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.unit.html">()</a>, Self::<a class="associatedtype" href="trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>&gt;<br>&nbsp;&nbsp;&nbsp; <span class="where">where<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;K: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a>,<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;V: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a></span>,
{ ... }
}</code></pre></div><details class="rustdoc-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 href="#example-use">Example use</a></h2>
<div class='information'><div class='tooltip edition' data-edition="2018"></div></div><div class="example-wrap"><pre class="rust rust-example-rendered edition"><code><span class="kw">use</span> <span class="ident">serde::ser</span>::{<span class="ident">Serialize</span>, <span class="ident">Serializer</span>, <span class="ident">SerializeMap</span>};
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Serialize</span> <span class="kw">for</span> <span class="ident">HashMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>
<span class="kw">where</span>
<span class="ident">K</span>: <span class="ident">Serialize</span>,
<span class="ident">V</span>: <span class="ident">Serialize</span>,
{
<span class="kw">fn</span> <span class="ident">serialize</span><span class="op">&lt;</span><span class="ident">S</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">serializer</span>: <span class="ident">S</span>) -&gt; <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">S::Ok</span>, <span class="ident">S::Error</span><span class="op">&gt;</span>
<span class="kw">where</span>
<span class="ident">S</span>: <span class="ident">Serializer</span>,
{
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">serializer</span>.<span class="ident">serialize_map</span>(<span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">len</span>()))<span class="question-mark">?</span>;
<span class="kw">for</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="kw">in</span> <span class="self">self</span> {
<span class="ident">map</span>.<span class="ident">serialize_entry</span>(<span class="ident">k</span>, <span class="ident">v</span>)<span class="question-mark">?</span>;
}
<span class="ident">map</span>.<span class="ident">end</span>()
}
}</code></pre></div>
<h2 id="example-implementation"><a href="#example-implementation">Example implementation</a></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="small-section-header">Required Associated Types<a href="#required-associated-types" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle" open><summary><div id="associatedtype.Ok" class="method has-srclink"><div class="rightside"><a class="srclink" href="../../src/serde/ser/mod.rs.html#1795">source</a></div><h4 class="code-header">type <a href="#associatedtype.Ok" class="associatedtype">Ok</a></h4></div></summary><div class="docblock"><p>Must match the <code>Ok</code> type of our <code>Serializer</code>.</p>
</div></details><details class="rustdoc-toggle" open><summary><div id="associatedtype.Error" class="method has-srclink"><div class="rightside"><a class="srclink" href="../../src/serde/ser/mod.rs.html#1798">source</a></div><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></div></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="small-section-header">Required Methods<a href="#required-methods" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle" open><summary><div id="tymethod.serialize_key" class="method has-srclink"><div class="rightside"><a class="srclink" href="../../src/serde/ser/mod.rs.html#1806-1808">source</a></div><h4 class="code-header">fn <a href="#tymethod.serialize_key" class="fnname">serialize_key</a>&lt;T:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/1.64.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(&amp;mut self, key: <a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.reference.html">&amp;</a>T) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.64.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.64.0/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 fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;T: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a>,&nbsp;</span></h4></div></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="rustdoc-toggle" open><summary><div id="tymethod.serialize_value" class="method has-srclink"><div class="rightside"><a class="srclink" href="../../src/serde/ser/mod.rs.html#1816-1818">source</a></div><h4 class="code-header">fn <a href="#tymethod.serialize_value" class="fnname">serialize_value</a>&lt;T:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/1.64.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(&amp;mut self, value: <a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.reference.html">&amp;</a>T) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.64.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.64.0/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 fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;T: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a>,&nbsp;</span></h4></div></summary><div class="docblock"><p>Serialize a map value.</p>
<h5 id="panics"><a href="#panics">Panics</a></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="rustdoc-toggle" open><summary><div id="tymethod.end" class="method has-srclink"><div class="rightside"><a class="srclink" href="../../src/serde/ser/mod.rs.html#1851">source</a></div><h4 class="code-header">fn <a href="#tymethod.end" class="fnname">end</a>(self) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.64.0/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></div></summary><div class="docblock"><p>Finish serializing a map.</p>
</div></details></div><h2 id="provided-methods" class="small-section-header">Provided Methods<a href="#provided-methods" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle" open><summary><div id="method.serialize_entry" class="method has-srclink"><div class="rightside"><a class="srclink" href="../../src/serde/ser/mod.rs.html#1837-1848">source</a></div><h4 class="code-header">fn <a href="#method.serialize_entry" class="fnname">serialize_entry</a>&lt;K:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/1.64.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, V:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/1.64.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;&amp;mut self,<br>&nbsp;&nbsp;&nbsp;&nbsp;key: <a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.reference.html">&amp;</a>K,<br>&nbsp;&nbsp;&nbsp;&nbsp;value: <a class="primitive" href="https://doc.rust-lang.org/1.64.0/std/primitive.reference.html">&amp;</a>V<br>) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.64.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.64.0/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 fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;K: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a>,<br>&nbsp;&nbsp;&nbsp;&nbsp;V: <a class="trait" href="../trait.Serialize.html" title="trait serde::Serialize">Serialize</a>,&nbsp;</span></h4></div></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="implementors" class="small-section-header">Implementors<a href="#implementors" class="anchor"></a></h2><div class="item-list" id="implementors-list"><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-SerializeMap-for-Impossible%3COk%2C%20Error%3E" class="impl has-srclink"><span class="rightside"><a class="srclink" href="../../src/serde/ser/impossible.rs.html#148-174">source</a></span><a href="#impl-SerializeMap-for-Impossible%3COk%2C%20Error%3E" class="anchor"></a><h3 class="code-header in-band">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; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;Error: <a class="trait" href="trait.Error.html" title="trait serde::ser::Error">Error</a>,&nbsp;</span></h3></section></summary><div class="impl-items"><section id="associatedtype.Ok-1" class="associatedtype trait-impl has-srclink"><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 has-srclink"><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 type="text/javascript" src="../../implementors/serde/ser/trait.SerializeMap.js" data-ignore-extern-crates="" async></script></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="serde" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.64.0 (a55dd71d5 2022-09-19)" ></div></body></html>