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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="Add `skip_serializing_if` annotations to `Option` fields."><title>skip_serializing_none in serde_with_macros - 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_macros" 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 attr"><!--[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_macros/index.html">serde_with_macros</a><span class="version">2.3.3</span></h2></div><div class="sidebar-elems"></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_macros/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>Attribute Macro <a href="index.html">serde_with_macros</a>::<wbr><a class="attr" href="#">skip_serializing_none</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_macros/lib.rs.html#319-328">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><pre class="rust item-decl"><code>#[skip_serializing_none]</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Add <code>skip_serializing_if</code> annotations to <a href="https://doc.rust-lang.org/1.76.0/core/option/enum.Option.html" title="enum core::option::Option"><code>Option</code></a> fields.</p>
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<p>The attribute can be added to structs and enums.
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The <code>#[skip_serializing_none]</code> attribute must be placed <em>before</em> the <code>#[derive]</code> attribute.</p>
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<h2 id="example"><a href="#example">Example</a></h2>
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<p>JSON APIs sometimes have many optional values.
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Missing values should not be serialized, to keep the serialized format smaller.
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Such a data type might look like:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Serialize)]
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</span><span class="kw">struct </span>Data {
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<span class="attr">#[serde(skip_serializing_if = <span class="string">"Option::is_none"</span>)]
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</span>a: <span class="prelude-ty">Option</span><String>,
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<span class="attr">#[serde(skip_serializing_if = <span class="string">"Option::is_none"</span>)]
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</span>b: <span class="prelude-ty">Option</span><u64>,
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<span class="attr">#[serde(skip_serializing_if = <span class="string">"Option::is_none"</span>)]
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</span>c: <span class="prelude-ty">Option</span><String>,
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<span class="attr">#[serde(skip_serializing_if = <span class="string">"Option::is_none"</span>)]
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</span>d: <span class="prelude-ty">Option</span><bool>,
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}</code></pre></div>
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<p>The <code>skip_serializing_if</code> annotation is repetitive and harms readability.
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Instead, the same struct can be written as:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[skip_serializing_none]
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#[derive(Serialize)]
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</span><span class="kw">struct </span>Data {
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a: <span class="prelude-ty">Option</span><String>,
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b: <span class="prelude-ty">Option</span><u64>,
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c: <span class="prelude-ty">Option</span><String>,
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<span class="comment">// Always serialize field d even if None
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</span><span class="attr">#[serialize_always]
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</span>d: <span class="prelude-ty">Option</span><bool>,
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}</code></pre></div>
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<p>Existing <code>skip_serializing_if</code> annotations will not be altered.</p>
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<p>If some values should always be serialized, then <code>serialize_always</code> can be used.</p>
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<h2 id="limitations"><a href="#limitations">Limitations</a></h2>
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<p>The <code>serialize_always</code> cannot be used together with a manual <code>skip_serializing_if</code> annotations,
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as these conflict in their meaning. A compile error will be generated if this occurs.</p>
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<p>The <code>skip_serializing_none</code> only works if the type is called <a href="https://doc.rust-lang.org/1.76.0/core/option/enum.Option.html" title="enum core::option::Option"><code>Option</code></a>,
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<a href="https://doc.rust-lang.org/1.76.0/core/option/enum.Option.html" title="enum core::option::Option"><code>std::option::Option</code></a>, or <a href="https://doc.rust-lang.org/1.76.0/core/option/enum.Option.html" title="enum core::option::Option"><code>core::option::Option</code></a>. Type aliasing an <a href="https://doc.rust-lang.org/1.76.0/core/option/enum.Option.html" title="enum core::option::Option"><code>Option</code></a> and giving it
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another name, will cause this field to be ignored. This cannot be supported, as proc-macros run
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before type checking, thus it is not possible to determine if a type alias refers to an
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<a href="https://doc.rust-lang.org/1.76.0/core/option/enum.Option.html" title="enum core::option::Option"><code>Option</code></a>.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">type </span>MyOption<T> = <span class="prelude-ty">Option</span><T>;
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<span class="attr">#[skip_serializing_none]
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#[derive(Serialize)]
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</span><span class="kw">struct </span>Data {
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a: MyOption<String>, <span class="comment">// This field will not be skipped
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</span>}</code></pre></div>
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<p>Likewise, if you import a type and name it <code>Option</code>, the <code>skip_serializing_if</code> attributes will
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be added and compile errors will occur, if <code>Option::is_none</code> is not a valid function.
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Here the function <code>Vec::is_none</code> does not exist, and therefore the example fails to compile.</p>
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<div class="example-wrap compile_fail"><a href="#" class="tooltip" title="This example deliberately fails to compile">ⓘ</a><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::vec::Vec <span class="kw">as </span><span class="prelude-ty">Option</span>;
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<span class="attr">#[skip_serializing_none]
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#[derive(Serialize)]
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</span><span class="kw">struct </span>Data {
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a: <span class="prelude-ty">Option</span><String>,
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}</code></pre></div>
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</div></details></section></div></main></body></html> |