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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="Apply attributes to all fields with matching types"><title>apply 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="#">apply</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#1316-1318">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><pre class="rust item-decl"><code>#[apply]</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Apply attributes to all fields with matching types</p>
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<p>Whenever you experience the need to apply the same attributes to multiple fields, you can use
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this macro. It allows you to specify a list of types and a list of attributes.
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Each field with a “matching” type will then get the attributes applied.
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The <code>apply</code> attribute must be place <em>before</em> any consuming attributes, such as <code>derive</code>, because
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Rust expands all attributes in order.</p>
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<p>For example, if your struct or enum contains many <code>Option<T></code> fields, but you do not want to
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serialize <code>None</code> values, you can use this macro to apply the <code>#[serde(skip_serializing_if = "Option::is_none")]</code> attribute to all fields of type <code>Option<T></code>.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[serde_with::apply(
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<span class="prelude-ty">Option </span>=> <span class="attr">#[serde(skip_serializing_if = <span class="string">"Option::is_none"</span>)]</span>,
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)]
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<span class="attr">#[derive(serde::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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d: <span class="prelude-ty">Option</span><bool>,
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}</code></pre></div>
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<p>Each rule starts with a type pattern, specifying which fields to match and a list of attributes
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to apply. Multiple rules can be provided in a single <code>apply</code> attribute.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[serde_with::apply(
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<span class="prelude-ty">Option </span>=> <span class="attr">#[serde(default)] #[serde(skip_serializing_if = <span class="string">"Option::is_none"</span>)]</span>,
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<span class="prelude-ty">Option</span><bool> => <span class="attr">#[serde(rename = <span class="string">"bool"</span>)]</span>,
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)]</code></pre></div>
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<h3 id="type-patterns"><a href="#type-patterns">Type Patterns</a></h3>
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<p>The type pattern left of the <code>=></code> specifies which fields to match.</p>
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<div><table><thead><tr><th style="text-align: left">Type Pattern</th><th style="text-align: right">Matching Types</th><th style="text-align: left">Notes</th></tr></thead><tbody>
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<tr><td style="text-align: left"><code>_</code></td><td style="text-align: right"><code>Option<bool></code><br><code>BTreeMap<&'static str, Vec<u32>></code></td><td style="text-align: left"><code>_</code> matches all fields.</td></tr>
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<tr><td style="text-align: left"><code>Option</code></td><td style="text-align: right"><code>Option<bool></code><br><code>Option<String></code></td><td style="text-align: left">A missing generic is compatible with any generic arguments.</td></tr>
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<tr><td style="text-align: left"><code>Option<bool></code></td><td style="text-align: right"><code>Option<bool></code></td><td style="text-align: left">A fully specified type only matches exactly.</td></tr>
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<tr><td style="text-align: left"><code>BTreeMap<String, u32></code></td><td style="text-align: right"><code>BTreeMap<String, u32></code></td><td style="text-align: left">A fully specified type only matches exactly.</td></tr>
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<tr><td style="text-align: left"><code>BTreeMap<String, _></code></td><td style="text-align: right"><code>BTreeMap<String, u32></code><br><code>BTreeMap<String, bool></code></td><td style="text-align: left">Any <code>String</code> key <code>BTreeMap</code> matches, as the value is using the <code>_</code> placeholder.</td></tr>
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<tr><td style="text-align: left"><code>[u8; _]</code></td><td style="text-align: right"><code>[u8; 1]</code><br><code>[u8; N]</code></td><td style="text-align: left"><code>_</code> also works as a placeholder for any array length.</td></tr>
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</tbody></table>
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</div><h3 id="opt-out-for-individual-fields"><a href="#opt-out-for-individual-fields">Opt-out for Individual Fields</a></h3>
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<p>The <code>apply</code> attribute will find all fields with a compatible type.
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This can be overly eager and a different set of attributes might be required for a specific
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field. You can opt-out of the <code>apply</code> attribute by adding the <code>#[serde_with(skip_apply)]</code>
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attribute to the field. This will prevent any <code>apply</code> to apply to this field.
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If two rules apply to the same field, it is impossible to opt-out of only a single one.
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In this case the attributes must be applied to the field manually.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[serde_with::apply(
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<span class="prelude-ty">Option </span>=> <span class="attr">#[serde(skip_serializing_if = <span class="string">"Option::is_none"</span>)]</span>,
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)]
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<span class="attr">#[derive(serde::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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<span class="attr">#[serde_with(skip_apply)]
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</span>always_serialize_this_field: <span class="prelude-ty">Option</span><u64>,
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c: <span class="prelude-ty">Option</span><String>,
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d: <span class="prelude-ty">Option</span><bool>,
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}
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<span class="kw">let </span>data = Data {
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a: <span class="prelude-val">None</span>,
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always_serialize_this_field: <span class="prelude-val">None</span>,
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c: <span class="prelude-val">None</span>,
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d: <span class="prelude-val">None</span>,
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};
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<span class="comment">// serializes into this JSON:
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</span>{
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<span class="string">"always_serialize_this_field"</span>: null
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}</code></pre></div>
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<h2 id="alternative-path-to-serde_with-crate"><a href="#alternative-path-to-serde_with-crate">Alternative path to <code>serde_with</code> crate</a></h2>
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<p>If <code>serde_with</code> is not available at the default path, its path should be specified with the
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<code>crate</code> argument. See [re-exporting <code>serde_as</code>] for more use case information.</p>
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<div class="example-wrap ignore"><a href="#" class="tooltip" title="This example is not tested">ⓘ</a><pre class="rust rust-example-rendered"><code><span class="attr">#[serde_with::apply(
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<span class="kw">crate </span>= <span class="string">"::some_other_lib::serde_with"
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</span><span class="prelude-ty">Option </span>=> <span class="attr">#[serde(skip_serializing_if = <span class="string">"Option::is_none"</span>)]</span>,
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)]
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<span class="attr">#[derive(serde::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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d: <span class="prelude-ty">Option</span><bool>,
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}</code></pre></div>
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</div></details></section></div></main></body></html> |