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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="Makes a distinction between a missing, unset, or existing value"><title>serde_with::rust::double_option - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../../static.files/rustdoc-ac92e1bbe349e143.css"><meta name="rustdoc-vars" data-root-path="../../../" data-static-root-path="../../../static.files/" data-current-crate="serde_with" data-themes="" data-resource-suffix="" data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)" data-channel="1.76.0" data-search-js="search-2b6ce74ff89ae146.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../../static.files/storage-f2adc0d6ca4d09fb.js"></script><script defer src="../sidebar-items.js"></script><script defer src="../../../static.files/main-305769736d49e732.js"></script><noscript><link rel="stylesheet" href="../../../static.files/noscript-feafe1bb7466e4bd.css"></noscript><link rel="alternate icon" type="image/png" href="../../../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc mod"><!--[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">☰</button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../../serde_with/index.html">serde_with</a><span class="version">2.3.3</span></h2></div><h2 class="location"><a href="#">Module double_option</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#functions">Functions</a></li></ul></section><h2><a href="../index.html">In serde_with::rust</a></h2></div></nav><div class="sidebar-resizer"></div>
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<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../../serde_with/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../../../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Module <a href="../../index.html">serde_with</a>::<wbr><a href="../index.html">rust</a>::<wbr><a class="mod" href="#">double_option</a><button id="copy-path" title="Copy item path to clipboard"><img src="../../../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../../../src/serde_with/rust.rs.html#60">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Makes a distinction between a missing, unset, or existing value</p>
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<p>Some serialization formats make a distinction between missing fields, fields with a <code>null</code>
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value, and existing values. One such format is JSON. By default it is not easily possible to
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differentiate between a missing value and a field which is <code>null</code>, as they deserialize to the
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same value. This helper changes it, by using an <code>Option<Option<T>></code> to deserialize into.</p>
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<ul>
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<li><code>None</code>: Represents a missing value.</li>
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<li><code>Some(None)</code>: Represents a <code>null</code> value.</li>
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<li><code>Some(Some(value))</code>: Represents an existing value.</li>
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</ul>
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<p>Note: This cannot be made compatible to <code>serde_as</code>, since skipping of values is only available on the field level.
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A hypothetical <code>DoubleOption<T></code> with a <code>SerializeAs</code> implementation would allow writing something like this.
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This cannot work, since there is no way to tell the <code>Vec</code> to skip the inner <code>DoubleOption</code> if it is <code>None</code>.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[serde_as(<span class="kw">as </span>= <span class="string">"Vec<DoubleOption<_>>"</span>)]
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</span>data: Vec<<span class="prelude-ty">Option</span><<span class="prelude-ty">Option</span><i32>>>,</code></pre></div>
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<h2 id="examples"><a href="#examples">Examples</a></h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Deserialize, Serialize)]
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</span><span class="kw">struct </span>Doc {
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<span class="attr">#[serde(
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default, <span class="comment">// <- important for deserialization
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</span>skip_serializing_if = <span class="string">"Option::is_none"</span>, <span class="comment">// <- important for serialization
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</span>with = <span class="string">"::serde_with::rust::double_option"</span>,
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)]
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</span>a: <span class="prelude-ty">Option</span><<span class="prelude-ty">Option</span><u8>>,
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}
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<span class="comment">// Missing Value
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</span><span class="kw">let </span>s = <span class="string">r#"{}"#</span>;
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<span class="macro">assert_eq!</span>(Doc { a: <span class="prelude-val">None </span>}, serde_json::from_str(s).unwrap());
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<span class="macro">assert_eq!</span>(s, serde_json::to_string(<span class="kw-2">&</span>Doc { a: <span class="prelude-val">None </span>}).unwrap());
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<span class="comment">// Unset Value
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</span><span class="kw">let </span>s = <span class="string">r#"{"a":null}"#</span>;
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<span class="macro">assert_eq!</span>(Doc { a: <span class="prelude-val">Some</span>(<span class="prelude-val">None</span>) }, serde_json::from_str(s).unwrap());
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<span class="macro">assert_eq!</span>(s, serde_json::to_string(<span class="kw-2">&</span>Doc { a: <span class="prelude-val">Some</span>(<span class="prelude-val">None</span>) }).unwrap());
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<span class="comment">// Existing Value
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</span><span class="kw">let </span>s = <span class="string">r#"{"a":5}"#</span>;
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<span class="macro">assert_eq!</span>(Doc { a: <span class="prelude-val">Some</span>(<span class="prelude-val">Some</span>(<span class="number">5</span>)) }, serde_json::from_str(s).unwrap());
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<span class="macro">assert_eq!</span>(s, serde_json::to_string(<span class="kw-2">&</span>Doc { a: <span class="prelude-val">Some</span>(<span class="prelude-val">Some</span>(<span class="number">5</span>)) }).unwrap());</code></pre></div>
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</div></details><h2 id="functions" class="section-header"><a href="#functions">Functions</a></h2><ul class="item-table"><li><div class="item-name"><a class="fn" href="fn.deserialize.html" title="fn serde_with::rust::double_option::deserialize">deserialize</a></div><div class="desc docblock-short">Deserialize potentially non-existing optional value</div></li><li><div class="item-name"><a class="fn" href="fn.serialize.html" title="fn serde_with::rust::double_option::serialize">serialize</a></div><div class="desc docblock-short">Serialize optional value</div></li></ul></section></div></main></body></html> |