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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 `VariantAccess` trait in crate `serde`."><meta name="keywords" content="rust, rustlang, rust-lang, VariantAccess"><title>serde::de::VariantAccess - 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="../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled ><script id="default-settings"></script><script src="../../storage.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../../favicon.svg">
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<link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><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">&#9776;</div><a href='../../serde/index.html'><div class='logo-container rust-logo'><img src='../../rust-logo.png' alt='logo'></div></a><p class="location">Trait VariantAccess</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.Error">Error</a></div><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.struct_variant">struct_variant</a><a href="#tymethod.unit_variant">unit_variant</a><a href="#tymethod.newtype_variant_seed">newtype_variant_seed</a><a href="#tymethod.tuple_variant">tuple_variant</a></div><a class="sidebar-title" href="#provided-methods">Provided Methods</a><div class="sidebar-links"><a href="#method.newtype_variant">newtype_variant</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">de</a></p><div id="sidebar-vars" data-name="VariantAccess" data-ty="trait" data-relpath=""></div><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices" role="menu"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press S to search, ? for more options…" type="search"></div><button type="button" class="help-button">?</button>
<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="in-band">Trait <a href="../index.html">serde</a>::<wbr><a href="index.html">de</a>::<wbr><a class="trait" href="">VariantAccess</a></span><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">&#x2212;</span>]</a></span><a class="srclink" href="../../src/serde/de/mod.rs.html#2004-2200" title="goto source code">[src]</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><pre class="rust trait">pub trait VariantAccess&lt;'de&gt;: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a> {
type <a href="#associatedtype.Error" class="type">Error</a>: <a class="trait" href="../../serde/de/trait.Error.html" title="trait serde::de::Error">Error</a>;
fn <a href="#tymethod.unit_variant" class="fnname">unit_variant</a>(self) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>&gt;;
<div class="item-spacer"></div> fn <a href="#tymethod.newtype_variant_seed" class="fnname">newtype_variant_seed</a>&lt;T&gt;(self, seed: T) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;T::<a class="type" href="../../serde/de/trait.DeserializeSeed.html#associatedtype.Value" title="type serde::de::DeserializeSeed::Value">Value</a>, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::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="../../serde/de/trait.DeserializeSeed.html" title="trait serde::de::DeserializeSeed">DeserializeSeed</a>&lt;'de&gt;</span>;
<div class="item-spacer"></div> fn <a href="#tymethod.tuple_variant" class="fnname">tuple_variant</a>&lt;V&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;len: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;visitor: V<br>&nbsp;&nbsp;&nbsp;&nbsp;) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;V::<a class="type" href="../../serde/de/trait.Visitor.html#associatedtype.Value" title="type serde::de::Visitor::Value">Value</a>, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>&gt;<br>&nbsp;&nbsp;&nbsp; <span class="where">where<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;V: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a>&lt;'de&gt;</span>;
<div class="item-spacer"></div> fn <a href="#tymethod.struct_variant" class="fnname">struct_variant</a>&lt;V&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fields: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&amp;'static [</a>&amp;'static <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.str.html">str</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">]</a>, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;visitor: V<br>&nbsp;&nbsp;&nbsp;&nbsp;) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;V::<a class="type" href="../../serde/de/trait.Visitor.html#associatedtype.Value" title="type serde::de::Visitor::Value">Value</a>, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>&gt;<br>&nbsp;&nbsp;&nbsp; <span class="where">where<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;V: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a>&lt;'de&gt;</span>;
fn <a href="#method.newtype_variant" class="fnname">newtype_variant</a>&lt;T&gt;(self) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;T, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::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="../../serde/trait.Deserialize.html" title="trait serde::Deserialize">Deserialize</a>&lt;'de&gt;</span>,
{ ... }
}</pre></div><div class="docblock"><p><code>VariantAccess</code> is a visitor that is created by the <code>Deserializer</code> and
passed to the <code>Deserialize</code> to deserialize the content of a particular enum
variant.</p>
<h1 id="lifetime" class="section-header"><a href="#lifetime">Lifetime</a></h1>
<p>The <code>'de</code> lifetime of this trait is the lifetime of data that may be
borrowed by the deserialized enum variant. See the page <a href="https://serde.rs/lifetimes.html">Understanding
deserializer lifetimes</a> for a more detailed explanation of these lifetimes.</p>
<h1 id="example-implementation" class="section-header"><a href="#example-implementation">Example implementation</a></h1>
<p>The <a href="https://serde.rs/data-format.html">example data format</a> presented on the website demonstrates an
implementation of <code>VariantAccess</code> for a basic JSON data format.</p>
</div><h2 id="associated-types" class="small-section-header">Associated Types<a href="#associated-types" class="anchor"></a></h2><div class="methods"><h3 id="associatedtype.Error" class="method"><code>type <a href="#associatedtype.Error" class="type">Error</a>: <a class="trait" href="../../serde/de/trait.Error.html" title="trait serde::de::Error">Error</a></code><a class="srclink" href="../../src/serde/de/mod.rs.html#2007" title="goto source code">[src]</a></h3><div class="docblock"><p>The error type that can be returned if some error occurs during
deserialization. Must match the error type of our <code>EnumAccess</code>.</p>
</div></div><span class="loading-content">Loading content...</span><h2 id="required-methods" class="small-section-header">Required methods<a href="#required-methods" class="anchor"></a></h2><div class="methods"><h3 id="tymethod.unit_variant" class="method"><code>fn <a href="#tymethod.unit_variant" class="fnname">unit_variant</a>(self) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>&gt;</code><a class="srclink" href="../../src/serde/de/mod.rs.html#2044" title="goto source code">[src]</a></h3><div class="docblock"><p>Called when deserializing a variant with no values.</p>
<p>If the data contains a different type of variant, the following
<code>invalid_type</code> error should be constructed:</p>
<div class='information'><div class='tooltip edition' data-edition="2018"></div></div><div class="example-wrap"><pre class="rust rust-example-rendered edition">
<span class="kw">fn</span> <span class="ident">unit_variant</span>(<span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span>(), <span class="self">Self</span>::<span class="ident">Error</span><span class="op">&gt;</span> {
<span class="comment">// What the data actually contained; suppose it is a tuple variant.</span>
<span class="kw">let</span> <span class="ident">unexp</span> <span class="op">=</span> <span class="ident">Unexpected</span>::<span class="ident">TupleVariant</span>;
<span class="prelude-val">Err</span>(<span class="ident">de</span>::<span class="ident">Error</span>::<span class="ident">invalid_type</span>(<span class="ident">unexp</span>, <span class="kw-2">&amp;</span><span class="string">&quot;unit variant&quot;</span>))
}</pre></div>
</div><h3 id="tymethod.newtype_variant_seed" class="method"><code>fn <a href="#tymethod.newtype_variant_seed" class="fnname">newtype_variant_seed</a>&lt;T&gt;(self, seed: T) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;T::<a class="type" href="../../serde/de/trait.DeserializeSeed.html#associatedtype.Value" title="type serde::de::DeserializeSeed::Value">Value</a>, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;T: <a class="trait" href="../../serde/de/trait.DeserializeSeed.html" title="trait serde::de::DeserializeSeed">DeserializeSeed</a>&lt;'de&gt;,&nbsp;</span></code><a class="srclink" href="../../src/serde/de/mod.rs.html#2086-2088" title="goto source code">[src]</a></h3><div class="docblock"><p>Called when deserializing a variant with a single value.</p>
<p><code>Deserialize</code> implementations should typically use
<code>VariantAccess::newtype_variant</code> instead.</p>
<p>If the data contains a different type of variant, the following
<code>invalid_type</code> error should be constructed:</p>
<div class='information'><div class='tooltip edition' data-edition="2018"></div></div><div class="example-wrap"><pre class="rust rust-example-rendered edition">
<span class="kw">fn</span> <span class="ident">newtype_variant_seed</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>(<span class="self">self</span>, <span class="ident">_seed</span>: <span class="ident">T</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">T</span>::<span class="ident">Value</span>, <span class="self">Self</span>::<span class="ident">Error</span><span class="op">&gt;</span>
<span class="kw">where</span>
<span class="ident">T</span>: <span class="ident">DeserializeSeed</span><span class="op">&lt;</span><span class="lifetime">&#39;de</span><span class="op">&gt;</span>,
{
<span class="comment">// What the data actually contained; suppose it is a unit variant.</span>
<span class="kw">let</span> <span class="ident">unexp</span> <span class="op">=</span> <span class="ident">Unexpected</span>::<span class="ident">UnitVariant</span>;
<span class="prelude-val">Err</span>(<span class="ident">de</span>::<span class="ident">Error</span>::<span class="ident">invalid_type</span>(<span class="ident">unexp</span>, <span class="kw-2">&amp;</span><span class="string">&quot;newtype variant&quot;</span>))
}</pre></div>
</div><h3 id="tymethod.tuple_variant" class="method"><code>fn <a href="#tymethod.tuple_variant" class="fnname">tuple_variant</a>&lt;V&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;len: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>, <br>&nbsp;&nbsp;&nbsp;&nbsp;visitor: V<br>) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;V::<a class="type" href="../../serde/de/trait.Visitor.html#associatedtype.Value" title="type serde::de::Visitor::Value">Value</a>, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;V: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a>&lt;'de&gt;,&nbsp;</span></code><a class="srclink" href="../../src/serde/de/mod.rs.html#2146-2148" title="goto source code">[src]</a></h3><div class="docblock"><p>Called when deserializing a tuple-like variant.</p>
<p>The <code>len</code> is the number of fields expected in the tuple variant.</p>
<p>If the data contains a different type of variant, the following
<code>invalid_type</code> error should be constructed:</p>
<div class='information'><div class='tooltip edition' data-edition="2018"></div></div><div class="example-wrap"><pre class="rust rust-example-rendered edition">
<span class="kw">fn</span> <span class="ident">tuple_variant</span><span class="op">&lt;</span><span class="ident">V</span><span class="op">&gt;</span>(
<span class="self">self</span>,
<span class="ident">_len</span>: <span class="ident">usize</span>,
<span class="ident">_visitor</span>: <span class="ident">V</span>,
) <span class="op">-</span><span class="op">&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">V</span>::<span class="ident">Value</span>, <span class="self">Self</span>::<span class="ident">Error</span><span class="op">&gt;</span>
<span class="kw">where</span>
<span class="ident">V</span>: <span class="ident">Visitor</span><span class="op">&lt;</span><span class="lifetime">&#39;de</span><span class="op">&gt;</span>,
{
<span class="comment">// What the data actually contained; suppose it is a unit variant.</span>
<span class="kw">let</span> <span class="ident">unexp</span> <span class="op">=</span> <span class="ident">Unexpected</span>::<span class="ident">UnitVariant</span>;
<span class="prelude-val">Err</span>(<span class="ident">de</span>::<span class="ident">Error</span>::<span class="ident">invalid_type</span>(<span class="ident">unexp</span>, <span class="kw-2">&amp;</span><span class="string">&quot;tuple variant&quot;</span>))
}</pre></div>
</div><h3 id="tymethod.struct_variant" class="method"><code>fn <a href="#tymethod.struct_variant" class="fnname">struct_variant</a>&lt;V&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;fields: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&amp;'static [</a>&amp;'static <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.str.html">str</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">]</a>, <br>&nbsp;&nbsp;&nbsp;&nbsp;visitor: V<br>) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;V::<a class="type" href="../../serde/de/trait.Visitor.html#associatedtype.Value" title="type serde::de::Visitor::Value">Value</a>, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;V: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a>&lt;'de&gt;,&nbsp;</span></code><a class="srclink" href="../../src/serde/de/mod.rs.html#2193-2199" title="goto source code">[src]</a></h3><div class="docblock"><p>Called when deserializing a struct-like variant.</p>
<p>The <code>fields</code> are the names of the fields of the struct variant.</p>
<p>If the data contains a different type of variant, the following
<code>invalid_type</code> error should be constructed:</p>
<div class='information'><div class='tooltip edition' data-edition="2018"></div></div><div class="example-wrap"><pre class="rust rust-example-rendered edition">
<span class="kw">fn</span> <span class="ident">struct_variant</span><span class="op">&lt;</span><span class="ident">V</span><span class="op">&gt;</span>(
<span class="self">self</span>,
<span class="ident">_fields</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;static</span> [<span class="kw-2">&amp;</span><span class="lifetime">&#39;static</span> <span class="ident">str</span>],
<span class="ident">_visitor</span>: <span class="ident">V</span>,
) <span class="op">-</span><span class="op">&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">V</span>::<span class="ident">Value</span>, <span class="self">Self</span>::<span class="ident">Error</span><span class="op">&gt;</span>
<span class="kw">where</span>
<span class="ident">V</span>: <span class="ident">Visitor</span><span class="op">&lt;</span><span class="lifetime">&#39;de</span><span class="op">&gt;</span>,
{
<span class="comment">// What the data actually contained; suppose it is a unit variant.</span>
<span class="kw">let</span> <span class="ident">unexp</span> <span class="op">=</span> <span class="ident">Unexpected</span>::<span class="ident">UnitVariant</span>;
<span class="prelude-val">Err</span>(<span class="ident">de</span>::<span class="ident">Error</span>::<span class="ident">invalid_type</span>(<span class="ident">unexp</span>, <span class="kw-2">&amp;</span><span class="string">&quot;struct variant&quot;</span>))
}</pre></div>
</div></div><span class="loading-content">Loading content...</span><h2 id="provided-methods" class="small-section-header">Provided methods<a href="#provided-methods" class="anchor"></a></h2><div class="methods"><h3 id="method.newtype_variant" class="method"><code>fn <a href="#method.newtype_variant" class="fnname">newtype_variant</a>&lt;T&gt;(self) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;T, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;T: <a class="trait" href="../../serde/trait.Deserialize.html" title="trait serde::Deserialize">Deserialize</a>&lt;'de&gt;,&nbsp;</span></code><a class="srclink" href="../../src/serde/de/mod.rs.html#2096-2101" title="goto source code">[src]</a></h3><div class="docblock"><p>Called when deserializing a variant with a single value.</p>
<p>This method exists as a convenience for <code>Deserialize</code> implementations.
<code>VariantAccess</code> implementations should not override the default
behavior.</p>
</div></div><span class="loading-content">Loading content...</span><h2 id="implementors" class="small-section-header">Implementors<a href="#implementors" class="anchor"></a></h2><div class="item-list" id="implementors-list"></div><span class="loading-content">Loading content...</span><script type="text/javascript" src="../../implementors/serde/de/trait.VariantAccess.js" async></script></section><section id="search" class="content hidden"></section><section class="footer"></section><div id="rustdoc-vars" data-root-path="../../" data-current-crate="serde"></div>
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