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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 `Expected` trait in crate `serde`."><meta name="keywords" content="rust, rustlang, rust-lang, Expected"><title>serde::de::Expected - 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 Expected</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.fmt">fmt</a></div><a class="sidebar-title" href="#foreign-impls">Implementations on Foreign Types</a><div class="sidebar-links"><a href="#impl-Expected-for-%26%27a%20str">&'a str</a></div><a class="sidebar-title" href="#implementors">Implementors</a><a class="sidebar-title" href="#implementations">Trait Implementations</a><div class="sidebar-links"><a href="#impl-Display">Display</a></div></div><p class='location'><a href='../index.html'>serde</a>::<wbr><a href='index.html'>de</a></p><script>window.sidebarCurrent = {name: 'Expected', 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#463-467' 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=''>Expected</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><pre class='rust trait'>pub trait Expected {
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fn <a href='#tymethod.fmt' class='fnname'>fmt</a>(&self, formatter: &mut <a class="struct" href="https://doc.rust-lang.org/nightly/core/fmt/struct.Formatter.html" title="struct core::fmt::Formatter">Formatter</a>) -> <a class="type" href="https://doc.rust-lang.org/nightly/core/fmt/type.Result.html" title="type core::fmt::Result">Result</a>;
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}</pre></div><div class='docblock'><p><code>Expected</code> represents an explanation of what data a <code>Visitor</code> was expecting
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to receive.</p>
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<p>This is used as an argument to the <code>invalid_type</code>, <code>invalid_value</code>, and
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<code>invalid_length</code> methods of the <code>Error</code> trait to build error messages. The
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message should be a noun or noun phrase that completes the sentence "This
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Visitor expects to receive ...", for example the message could be "an
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integer between 0 and 64". The message should not be capitalized and should
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not end with a period.</p>
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<p>Within the context of a <code>Visitor</code> implementation, the <code>Visitor</code> itself
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(<code>&self</code>) is an implementation of this trait.</p>
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<pre><code class="language-edition2018"># use std::fmt;
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#
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# use serde::de::{self, Unexpected, Visitor};
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#
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# struct Example;
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#
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# impl<'de> Visitor<'de> for Example {
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# type Value = ();
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#
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# fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
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# write!(formatter, "definitely not a boolean")
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# }
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#
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fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Err(de::Error::invalid_type(Unexpected::Bool(v), &self))
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}
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# }
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</code></pre>
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<p>Outside of a <code>Visitor</code>, <code>&"..."</code> can be used.</p>
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<pre><code class="language-edition2018"># use serde::de::{self, Unexpected};
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#
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# fn example<E>() -> Result<(), E>
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# where
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# E: de::Error,
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# {
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# let v = true;
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return Err(de::Error::invalid_type(Unexpected::Bool(v), &"a negative integer"));
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# }
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</code></pre>
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</div>
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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.fmt' class='method'><code id='fmt.v'>fn <a href='#tymethod.fmt' class='fnname'>fmt</a>(&self, formatter: &mut <a class="struct" href="https://doc.rust-lang.org/nightly/core/fmt/struct.Formatter.html" title="struct core::fmt::Formatter">Formatter</a>) -> <a class="type" href="https://doc.rust-lang.org/nightly/core/fmt/type.Result.html" title="type core::fmt::Result">Result</a></code></h3><div class='docblock'><p>Format an explanation of what data was being expected. Same signature as
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the <code>Display</code> and <code>Debug</code> traits.</p>
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</div></div><span class='loading-content'>Loading content...</span><h2 id='implementations' class='small-section-header'>Trait Implementations<a href='#implementations' class='anchor'></a></h2><div id='implementations-list'><h3 id='impl-Display' class='impl'><code class='in-band'>impl<'a> <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Display.html" title="trait core::fmt::Display">Display</a> for dyn <a class="trait" href="../../serde/de/trait.Expected.html" title="trait serde::de::Expected">Expected</a> + 'a</code><a href='#impl-Display' class='anchor'></a><a class='srclink' href='../../src/serde/de/mod.rs.html#484-488' title='goto source code'>[src]</a></h3><div class='impl-items'><h4 id='method.fmt' class="method hidden"><code id='fmt.v-1'>fn <a href='https://doc.rust-lang.org/nightly/core/fmt/trait.Display.html#tymethod.fmt' class='fnname'>fmt</a>(&self, formatter: &mut <a class="struct" href="https://doc.rust-lang.org/nightly/core/fmt/struct.Formatter.html" title="struct core::fmt::Formatter">Formatter</a>) -> <a class="type" href="https://doc.rust-lang.org/nightly/core/fmt/type.Result.html" title="type core::fmt::Result">Result</a></code><a class='srclink' href='../../src/serde/de/mod.rs.html#485-487' title='goto source code'>[src]</a></h4><div class='docblock hidden'><p>Formats the value using the given formatter. <a href="https://doc.rust-lang.org/nightly/core/fmt/trait.Display.html#tymethod.fmt">Read more</a></p>
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</div></div></div>
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<h2 id='foreign-impls' class='small-section-header'>Implementations on Foreign Types<a href='#foreign-impls' class='anchor'></a></h2><h3 id='impl-Expected-for-%26%27a%20str' class='impl'><code class='in-band'>impl<'a> <a class="trait" href="../../serde/de/trait.Expected.html" title="trait serde::de::Expected">Expected</a> for &'a <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.str.html">str</a></code><a href='#impl-Expected-for-%26%27a%20str' class='anchor'></a><a class='srclink' href='../../src/serde/de/mod.rs.html#478-482' title='goto source code'>[src]</a></h3><div class='impl-items'><h4 id='method.fmt-1' class="method hidden"><code id='fmt.v-2'>fn <a href='#method.fmt' class='fnname'>fmt</a>(&self, formatter: &mut <a class="struct" href="https://doc.rust-lang.org/nightly/core/fmt/struct.Formatter.html" title="struct core::fmt::Formatter">Formatter</a>) -> <a class="type" href="https://doc.rust-lang.org/nightly/core/fmt/type.Result.html" title="type core::fmt::Result">Result</a></code><a class='srclink' href='../../src/serde/de/mod.rs.html#479-481' title='goto source code'>[src]</a></h4></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-Expected' class='impl'><code class='in-band'>impl<'de, T> Expected for T <span class="where fmt-newline">where<br> T: <a class="trait" href="../../serde/de/trait.Visitor.html" title="trait serde::de::Visitor">Visitor</a><'de>, </span></code><a href='#impl-Expected' class='anchor'></a><a class='srclink' href='../../src/serde/de/mod.rs.html#469-476' title='goto source code'>[src]</a></h3><div class='impl-items'><h4 id='method.fmt-2' class="method hidden"><code id='fmt.v-3'>fn <a href='#method.fmt-2' class='fnname'>fmt</a>(&self, formatter: &mut <a class="struct" href="https://doc.rust-lang.org/nightly/core/fmt/struct.Formatter.html" title="struct core::fmt::Formatter">Formatter</a>) -> <a class="type" href="https://doc.rust-lang.org/nightly/core/fmt/type.Result.html" title="type core::fmt::Result">Result</a></code><a class='srclink' href='../../src/serde/de/mod.rs.html#473-475' 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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