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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="../../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 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.newtype_variant_seed">newtype_variant_seed</a><a href="#tymethod.struct_variant">struct_variant</a><a href="#tymethod.tuple_variant">tuple_variant</a><a href="#tymethod.unit_variant">unit_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><script>window.sidebarCurrent = {name: 'VariantAccess', 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/de/mod.rs.html#1998-2194' title='goto source code'>[src]</a></span><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></h1><div class="docblock type-decl hidden-by-usual-hider"><pre class='rust trait'>pub trait VariantAccess<'de>: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a> {
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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>;
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fn <a href='#tymethod.unit_variant' class='fnname'>unit_variant</a>(self) -> <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/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>>;
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<div class='item-spacer'></div> fn <a href='#tymethod.newtype_variant_seed' class='fnname'>newtype_variant_seed</a><T>(self, seed: T) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><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>><br> <span class="where">where<br> T: <a class="trait" href="../../serde/de/trait.DeserializeSeed.html" title="trait serde::de::DeserializeSeed">DeserializeSeed</a><'de></span>;
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<div class='item-spacer'></div> fn <a href='#tymethod.tuple_variant' class='fnname'>tuple_variant</a><V>(<br> self, <br> len: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>, <br> visitor: V<br> ) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><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>><br> <span class="where">where<br> V: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a><'de></span>;
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<div class='item-spacer'></div> fn <a href='#tymethod.struct_variant' class='fnname'>struct_variant</a><V>(<br> self, <br> fields: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&'static [</a>&'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> visitor: V<br> ) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><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>><br> <span class="where">where<br> V: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a><'de></span>;
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fn <a href='#method.newtype_variant' class='fnname'>newtype_variant</a><T>(self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><T, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>><br> <span class="where">where<br> T: <a class="trait" href="../../serde/trait.Deserialize.html" title="trait serde::Deserialize">Deserialize</a><'de></span>,
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{ ... }
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}</pre></div><div class='docblock'><p><code>VariantAccess</code> is a visitor that is created by the <code>Deserializer</code> and
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passed to the <code>Deserialize</code> to deserialize the content of a particular enum
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variant.</p>
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<h1 id="lifetime" class="section-header"><a href="#lifetime">Lifetime</a></h1>
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<p>The <code>'de</code> lifetime of this trait is the lifetime of data that may be
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borrowed by the deserialized enum variant. See the page <a href="https://serde.rs/lifetimes.html">Understanding
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deserializer lifetimes</a> for a more detailed explanation of these lifetimes.</p>
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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>VariantAccess</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.Error' class='method'><code id='Error.t'>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></h3><div class='docblock'><p>The error type that can be returned if some error occurs during
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deserialization. Must match the error type of our <code>EnumAccess</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.unit_variant' class='method'><code id='unit_variant.v'>fn <a href='#tymethod.unit_variant' class='fnname'>unit_variant</a>(self) -> <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/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>></code></h3><div class='docblock'><p>Called when deserializing a variant with no values.</p>
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<p>If the data contains a different type of variant, the following
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<code>invalid_type</code> error should be constructed:</p>
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<pre><code class="language-edition2018"># use serde::de::{self, value, DeserializeSeed, Visitor, VariantAccess, Unexpected};
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#
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# struct X;
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#
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# impl<'de> VariantAccess<'de> for X {
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# type Error = value::Error;
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#
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fn unit_variant(self) -> Result<(), Self::Error> {
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// What the data actually contained; suppose it is a tuple variant.
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let unexp = Unexpected::TupleVariant;
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Err(de::Error::invalid_type(unexp, &"unit variant"))
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}
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#
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# fn newtype_variant_seed<T>(self, _: T) -> Result<T::Value, Self::Error>
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# where
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# T: DeserializeSeed<'de>,
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# { unimplemented!() }
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#
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# fn tuple_variant<V>(self, _: usize, _: V) -> Result<V::Value, Self::Error>
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# where
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# V: Visitor<'de>,
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# { unimplemented!() }
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#
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# fn struct_variant<V>(self, _: &[&str], _: V) -> Result<V::Value, Self::Error>
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# where
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# V: Visitor<'de>,
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# { unimplemented!() }
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# }
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</code></pre>
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</div><h3 id='tymethod.newtype_variant_seed' class='method'><code id='newtype_variant_seed.v'>fn <a href='#tymethod.newtype_variant_seed' class='fnname'>newtype_variant_seed</a><T>(self, seed: T) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><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>> <span class="where fmt-newline">where<br> T: <a class="trait" href="../../serde/de/trait.DeserializeSeed.html" title="trait serde::de::DeserializeSeed">DeserializeSeed</a><'de>, </span></code></h3><div class='docblock'><p>Called when deserializing a variant with a single value.</p>
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<p><code>Deserialize</code> implementations should typically use
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<code>VariantAccess::newtype_variant</code> instead.</p>
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<p>If the data contains a different type of variant, the following
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<code>invalid_type</code> error should be constructed:</p>
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<pre><code class="language-edition2018"># use serde::de::{self, value, DeserializeSeed, Visitor, VariantAccess, Unexpected};
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#
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# struct X;
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#
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# impl<'de> VariantAccess<'de> for X {
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# type Error = value::Error;
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#
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# fn unit_variant(self) -> Result<(), Self::Error> {
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# unimplemented!()
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# }
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#
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fn newtype_variant_seed<T>(self, _seed: T) -> Result<T::Value, Self::Error>
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where
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T: DeserializeSeed<'de>,
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{
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// What the data actually contained; suppose it is a unit variant.
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let unexp = Unexpected::UnitVariant;
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Err(de::Error::invalid_type(unexp, &"newtype variant"))
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}
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#
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# fn tuple_variant<V>(self, _: usize, _: V) -> Result<V::Value, Self::Error>
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# where
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# V: Visitor<'de>,
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# { unimplemented!() }
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#
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# fn struct_variant<V>(self, _: &[&str], _: V) -> Result<V::Value, Self::Error>
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# where
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# V: Visitor<'de>,
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# { unimplemented!() }
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# }
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</code></pre>
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</div><h3 id='tymethod.tuple_variant' class='method'><code id='tuple_variant.v'>fn <a href='#tymethod.tuple_variant' class='fnname'>tuple_variant</a><V>(<br> self, <br> len: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>, <br> visitor: V<br>) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><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>> <span class="where fmt-newline">where<br> V: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a><'de>, </span></code></h3><div class='docblock'><p>Called when deserializing a tuple-like variant.</p>
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<p>The <code>len</code> is the number of fields expected in the tuple variant.</p>
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<p>If the data contains a different type of variant, the following
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<code>invalid_type</code> error should be constructed:</p>
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<pre><code class="language-edition2018"># use serde::de::{self, value, DeserializeSeed, Visitor, VariantAccess, Unexpected};
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#
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# struct X;
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#
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# impl<'de> VariantAccess<'de> for X {
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# type Error = value::Error;
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#
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# fn unit_variant(self) -> Result<(), Self::Error> {
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# unimplemented!()
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# }
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#
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# fn newtype_variant_seed<T>(self, _: T) -> Result<T::Value, Self::Error>
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# where
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# T: DeserializeSeed<'de>,
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# { unimplemented!() }
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#
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fn tuple_variant<V>(
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self,
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_len: usize,
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_visitor: V,
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) -> Result<V::Value, Self::Error>
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where
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V: Visitor<'de>,
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{
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// What the data actually contained; suppose it is a unit variant.
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let unexp = Unexpected::UnitVariant;
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Err(de::Error::invalid_type(unexp, &"tuple variant"))
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}
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#
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# fn struct_variant<V>(self, _: &[&str], _: V) -> Result<V::Value, Self::Error>
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# where
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# V: Visitor<'de>,
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# { unimplemented!() }
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# }
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</code></pre>
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</div><h3 id='tymethod.struct_variant' class='method'><code id='struct_variant.v'>fn <a href='#tymethod.struct_variant' class='fnname'>struct_variant</a><V>(<br> self, <br> fields: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&'static [</a>&'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> visitor: V<br>) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><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>> <span class="where fmt-newline">where<br> V: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a><'de>, </span></code></h3><div class='docblock'><p>Called when deserializing a struct-like variant.</p>
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<p>The <code>fields</code> are the names of the fields of the struct variant.</p>
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<p>If the data contains a different type of variant, the following
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<code>invalid_type</code> error should be constructed:</p>
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<pre><code class="language-edition2018"># use serde::de::{self, value, DeserializeSeed, Visitor, VariantAccess, Unexpected};
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#
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# struct X;
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#
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# impl<'de> VariantAccess<'de> for X {
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# type Error = value::Error;
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#
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# fn unit_variant(self) -> Result<(), Self::Error> {
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# unimplemented!()
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# }
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#
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# fn newtype_variant_seed<T>(self, _: T) -> Result<T::Value, Self::Error>
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# where
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# T: DeserializeSeed<'de>,
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# { unimplemented!() }
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#
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# fn tuple_variant<V>(self, _: usize, _: V) -> Result<V::Value, Self::Error>
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# where
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# V: Visitor<'de>,
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# { unimplemented!() }
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#
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fn struct_variant<V>(
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self,
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_fields: &'static [&'static str],
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_visitor: V,
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) -> Result<V::Value, Self::Error>
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where
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V: Visitor<'de>,
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{
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// What the data actually contained; suppose it is a unit variant.
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let unexp = Unexpected::UnitVariant;
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Err(de::Error::invalid_type(unexp, &"struct variant"))
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}
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# }
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</code></pre>
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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.newtype_variant' class='method'><code id='newtype_variant.v'>fn <a href='#method.newtype_variant' class='fnname'>newtype_variant</a><T>(self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><T, Self::<a class="type" href="../../serde/de/trait.VariantAccess.html#associatedtype.Error" title="type serde::de::VariantAccess::Error">Error</a>> <span class="where fmt-newline">where<br> T: <a class="trait" href="../../serde/trait.Deserialize.html" title="trait serde::Deserialize">Deserialize</a><'de>, </span></code></h3><div class='docblock'><p>Called when deserializing a variant with a single value.</p>
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<p>This method exists as a convenience for <code>Deserialize</code> implementations.
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<code>VariantAccess</code> implementations should not override the default
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behavior.</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'></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/de/trait.VariantAccess.js">
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