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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="API documentation for the Rust `SerializeMap` trait in crate `serde`."><meta name="keywords" content="rust, rustlang, rust-lang, SerializeMap"><title>serde::ser::SerializeMap - Rust</title><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="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="shortcut icon" href="../../favicon.ico"><style type="text/css">#crate-search{background-image:url("../../down-arrow.svg");}</style></head><body class="rustdoc trait"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../serde/index.html'><div class='logo-container'><img src='../../rust-logo.png' alt='logo'></div></a><p class='location'>Trait SerializeMap</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#associated-types">Associated Types</a><div class="sidebar-links"><a href="#associatedtype.Ok">Ok</a><a href="#associatedtype.Error">Error</a></div><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.end">end</a><a href="#tymethod.serialize_key">serialize_key</a><a href="#tymethod.serialize_value">serialize_value</a></div><a class="sidebar-title" href="#provided-methods">Provided Methods</a><div class="sidebar-links"><a href="#method.serialize_entry">serialize_entry</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>serde</a>::<wbr><a href='index.html'>ser</a></p><script>window.sidebarCurrent = {name: 'SerializeMap', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><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/serde/ser/mod.rs.html#1764-1823' title='goto source code'>[src]</a></span><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></span></h1><div class="docblock type-decl hidden-by-usual-hider"><pre class='rust trait'>pub trait SerializeMap {
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type <a href='#associatedtype.Ok' class="type">Ok</a>;
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type <a href='#associatedtype.Error' class="type">Error</a>: <a class="trait" href="../../serde/ser/trait.Error.html" title="trait serde::ser::Error">Error</a>;
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fn <a href='#tymethod.serialize_key' class='fnname'>serialize_key</a><T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, key: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>><br> <span class="where">where<br> T: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a></span>;
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<div class='item-spacer'></div> fn <a href='#tymethod.serialize_value' class='fnname'>serialize_value</a><T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> &mut self, <br> value: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T<br> ) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>><br> <span class="where">where<br> T: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a></span>;
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<div class='item-spacer'></div> fn <a href='#tymethod.end' class='fnname'>end</a>(self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Ok" title="type serde::ser::SerializeMap::Ok">Ok</a>, Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>>;
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fn <a href='#method.serialize_entry' class='fnname'>serialize_entry</a><K: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, V: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> &mut self, <br> key: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>K, <br> value: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>V<br> ) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>><br> <span class="where">where<br> K: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a>,<br> V: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a></span>,
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{ ... }
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}</pre></div><div class='docblock'><p>Returned from <code>Serializer::serialize_map</code>.</p>
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<h1 id="example-use" class="section-header"><a href="#example-use">Example use</a></h1>
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<pre><code class="language-edition2018"># use std::marker::PhantomData;
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#
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# struct HashMap<K, V>(PhantomData<K>, PhantomData<V>);
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#
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# impl<K, V> HashMap<K, V> {
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# fn len(&self) -> usize {
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# unimplemented!()
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# }
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# }
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#
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# impl<'a, K, V> IntoIterator for &'a HashMap<K, V> {
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# type Item = (&'a K, &'a V);
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# type IntoIter = Box<Iterator<Item = (&'a K, &'a V)>>;
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#
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# fn into_iter(self) -> Self::IntoIter {
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# unimplemented!()
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# }
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# }
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#
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use serde::ser::{Serialize, Serializer, SerializeMap};
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impl<K, V> Serialize for HashMap<K, V>
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where
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K: Serialize,
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V: Serialize,
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{
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fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
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where
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S: Serializer,
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{
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let mut map = serializer.serialize_map(Some(self.len()))?;
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for (k, v) in self {
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map.serialize_entry(k, v)?;
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}
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map.end()
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}
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}
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</code></pre>
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<h1 id="example-implementation" class="section-header"><a href="#example-implementation">Example implementation</a></h1>
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<p>The <a href="https://serde.rs/data-format.html">example data format</a> presented on the website demonstrates an
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implementation of <code>SerializeMap</code> for a basic JSON data format.</p>
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</div>
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<h2 id='associated-types' class='small-section-header'>Associated Types<a href='#associated-types' class='anchor'></a></h2><div class='methods'><h3 id='associatedtype.Ok' class='method'><code id='Ok.t'>type <a href='#associatedtype.Ok' class="type">Ok</a></code></h3><div class='docblock'><p>Must match the <code>Ok</code> type of our <code>Serializer</code>.</p>
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</div><h3 id='associatedtype.Error' class='method'><code id='Error.t'>type <a href='#associatedtype.Error' class="type">Error</a>: <a class="trait" href="../../serde/ser/trait.Error.html" title="trait serde::ser::Error">Error</a></code></h3><div class='docblock'><p>Must match the <code>Error</code> type of our <code>Serializer</code>.</p>
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</div></div><span class='loading-content'>Loading content...</span>
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<h2 id='required-methods' class='small-section-header'>Required methods<a href='#required-methods' class='anchor'></a></h2><div class='methods'><h3 id='tymethod.serialize_key' class='method'><code id='serialize_key.v'>fn <a href='#tymethod.serialize_key' class='fnname'>serialize_key</a><T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, key: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>> <span class="where fmt-newline">where<br> T: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a>, </span></code></h3><div class='docblock'><p>Serialize a map key.</p>
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<p>If possible, <code>Serialize</code> implementations are encouraged to use
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<code>serialize_entry</code> instead as it may be implemented more efficiently in
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some formats compared to a pair of calls to <code>serialize_key</code> and
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<code>serialize_value</code>.</p>
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</div><h3 id='tymethod.serialize_value' class='method'><code id='serialize_value.v'>fn <a href='#tymethod.serialize_value' class='fnname'>serialize_value</a><T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, value: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>> <span class="where fmt-newline">where<br> T: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a>, </span></code></h3><div class='docblock'><p>Serialize a map value.</p>
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<h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1>
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<p>Calling <code>serialize_value</code> before <code>serialize_key</code> is incorrect and is
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allowed to panic or produce bogus results.</p>
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</div><h3 id='tymethod.end' class='method'><code id='end.v'>fn <a href='#tymethod.end' class='fnname'>end</a>(self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Ok" title="type serde::ser::SerializeMap::Ok">Ok</a>, Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>></code></h3><div class='docblock'><p>Finish serializing a map.</p>
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</div></div><span class='loading-content'>Loading content...</span>
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<h2 id='provided-methods' class='small-section-header'>Provided methods<a href='#provided-methods' class='anchor'></a></h2><div class='methods'><h3 id='method.serialize_entry' class='method'><code id='serialize_entry.v'>fn <a href='#method.serialize_entry' class='fnname'>serialize_entry</a><K: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, V: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> &mut self, <br> key: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>K, <br> value: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>V<br>) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Self::<a class="type" href="../../serde/ser/trait.SerializeMap.html#associatedtype.Error" title="type serde::ser::SerializeMap::Error">Error</a>> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a>,<br> V: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a>, </span></code></h3><div class='docblock'><p>Serialize a map entry consisting of a key and a value.</p>
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<p>Some <a href="../trait.Serialize.html"><code>Serialize</code></a> types are not able to hold a key and value in memory
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at the same time so <code>SerializeMap</code> implementations are required to
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support <a href="#tymethod.serialize_key"><code>serialize_key</code></a> and <a href="#tymethod.serialize_value"><code>serialize_value</code></a> individually. The
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<code>serialize_entry</code> method allows serializers to optimize for the case
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where key and value are both available. <a href="../trait.Serialize.html"><code>Serialize</code></a> implementations
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are encouraged to use <code>serialize_entry</code> if possible.</p>
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<p>The default implementation delegates to <a href="#tymethod.serialize_key"><code>serialize_key</code></a> and
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<a href="#tymethod.serialize_value"><code>serialize_value</code></a>. This is appropriate for serializers that do not
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care about performance or are not able to optimize <code>serialize_entry</code> any
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better than this.</p>
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</div></div><span class='loading-content'>Loading content...</span>
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<h2 id='implementors' class='small-section-header'>Implementors<a href='#implementors' class='anchor'></a></h2><div class='item-list' id='implementors-list'><h3 id='impl-SerializeMap' class='impl'><code class='in-band'>impl<Ok, Error> SerializeMap for <a class="struct" href="../../serde/ser/struct.Impossible.html" title="struct serde::ser::Impossible">Impossible</a><Ok, Error> <span class="where fmt-newline">where<br> Error: <a class="trait" href="../../serde/ser/trait.Error.html" title="trait serde::ser::Error">Error</a>, </span></code><a href='#impl-SerializeMap' class='anchor'></a><a class='srclink' href='../../src/serde/ser/impossible.rs.html#148-174' title='goto source code'>[src]</a></h3><div class='impl-items'><h4 id='associatedtype.Ok-1' class="type"><code id='Ok.t-1'>type <a href='#associatedtype.Ok-1' class="type">Ok</a> = Ok</code></h4><h4 id='associatedtype.Error-1' class="type"><code id='Error.t-1'>type <a href='#associatedtype.Error-1' class="type">Error</a> = Error</code></h4><h4 id='method.serialize_key' class="method hidden"><code id='serialize_key.v-1'>fn <a href='#method.serialize_key' class='fnname'>serialize_key</a><T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, key: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Error> <span class="where fmt-newline">where<br> T: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a>, </span></code><a class='srclink' href='../../src/serde/ser/impossible.rs.html#155-161' title='goto source code'>[src]</a></h4><h4 id='method.serialize_value' class="method hidden"><code id='serialize_value.v-1'>fn <a href='#method.serialize_value' class='fnname'>serialize_value</a><T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, value: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Error> <span class="where fmt-newline">where<br> T: <a class="trait" href="../../serde/trait.Serialize.html" title="trait serde::Serialize">Serialize</a>, </span></code><a class='srclink' href='../../src/serde/ser/impossible.rs.html#163-169' title='goto source code'>[src]</a></h4><h4 id='method.end' class="method hidden"><code id='end.v-1'>fn <a href='#method.end' class='fnname'>end</a>(self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><Ok, Error></code><a class='srclink' href='../../src/serde/ser/impossible.rs.html#171-173' title='goto source code'>[src]</a></h4></div></div><span class='loading-content'>Loading content...</span><script type="text/javascript">window.inlined_types=new Set([]);</script><script type="text/javascript" async
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src="../../implementors/serde/ser/trait.SerializeMap.js">
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