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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="Traits and types used for tracking the usage of generic parameters through a proc-macro input."><title>darling_core::usage - 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="darling_core" 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="../../darling_core/index.html">darling_core</a><span class="version">0.20.3</span></h2></div><h2 class="location"><a href="#">Module usage</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li><li><a href="#traits">Traits</a></li><li><a href="#types">Type Aliases</a></li></ul></section><h2><a href="../index.html">In crate darling_core</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="../../darling_core/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">darling_core</a>::<wbr><a class="mod" href="#">usage</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/darling_core/usage/mod.rs.html#1-111">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>Traits and types used for tracking the usage of generic parameters through a proc-macro input.</p>
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<p>When generating trait impls, libraries often want to automatically figure out which type parameters
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are used in which fields, and then emit bounds that will produce the most permissive compilable
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code.</p>
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<h2 id="usage"><a href="#usage">Usage</a></h2><h3 id="example-1-filtering"><a href="#example-1-filtering">Example 1: Filtering</a></h3>
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<p>This example accepts a proc-macro input, then finds all lifetimes and type parameters used
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by private fields.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">fn </span>process(input: <span class="kw-2">&</span>DeriveInput) -> Generics {
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<span class="kw">let </span>type_params = input.generics.declared_type_params();
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<span class="kw">let </span>lifetimes = input.generics.declared_lifetimes();
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<span class="kw">let </span><span class="kw-2">mut </span>ret_generics = input.generics.clone();
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<span class="kw">if let </span>Data::Struct(<span class="kw-2">ref </span>body) = input.data {
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<span class="kw">let </span>internal_fields = body
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.fields
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.iter()
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.filter(|field| field.vis == Visibility::Inherited)
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.collect::<Vec<<span class="kw">_</span>>>();
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<span class="kw">let </span>int_type_params = internal_fields
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.collect_type_params(<span class="kw-2">&</span>Purpose::BoundImpl.into(), <span class="kw-2">&</span>type_params);
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<span class="comment">// We could reuse the vec from above, but here we'll instead
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// directly consume the chained iterator.
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</span><span class="kw">let </span>int_lifetimes = body
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.fields
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.iter()
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.filter(|field| field.vis == Visibility::Inherited)
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.collect_lifetimes(<span class="kw-2">&</span>Purpose::BoundImpl.into(), <span class="kw-2">&</span>lifetimes);
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ret_generics.params = ret_generics
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.params
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.into_iter()
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.filter(|gp| {
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<span class="kw">match </span><span class="kw-2">*</span>gp {
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GenericParam::Type(<span class="kw-2">ref </span>ty) => int_type_params.contains(<span class="kw-2">&</span>ty.ident),
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GenericParam::Lifetime(<span class="kw-2">ref </span>lt) => int_lifetimes.contains(<span class="kw-2">&</span>lt.lifetime),
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<span class="kw">_ </span>=> <span class="bool-val">true</span>,
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}
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})
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.collect();
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}
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ret_generics
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}
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</code></pre></div>
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<h3 id="example-2-integrating-with-fromderiveinput"><a href="#example-2-integrating-with-fromderiveinput">Example 2: Integrating with <code>FromDeriveInput</code></a></h3>
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<p>It is possible to use <code>darling</code>’s magic fields feature in tandem with the <code>usage</code> feature set.
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While there is no custom derive for <code>UsesTypeParams</code> or <code>UsesLifetimes</code>, there are macros to
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generate impls.</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">#![allow(dead_code)]
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#[derive(FromField)]
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#[darling(attributes(speak))]
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</span><span class="kw">struct </span>SpeakerField {
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ident: <span class="prelude-ty">Option</span><syn::Ident>,
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ty: syn::Type,
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<span class="attr">#[darling(default)]
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</span>volume: <span class="prelude-ty">Option</span><u32>,
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}
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<span class="macro">uses_type_params!</span>(SpeakerField, ty);
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<span class="macro">uses_lifetimes!</span>(SpeakerField, ty);
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<span class="attr">#[derive(FromDeriveInput)]
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</span><span class="kw">struct </span>SpeakerOptions {
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generics: syn::Generics,
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data: darling::ast::Data<darling::util::Ignored, SpeakerField>,
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}</code></pre></div>
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<p>At this point, you are able to call <code>uses_type_params</code> on <code>SpeakerOptions.data</code>, or any filtered
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view of it. <code>darling</code> internally uses this in conjunction with the <code>skip</code> meta-item to determine
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which type parameters don’t require the <code>FromMeta</code> bound in generated impls.</p>
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<p><strong>Note:</strong> If you are performing operations referencing generic params in meta-items parsed by <code>darling</code>,
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you should determine if those impact the emitted code and wire up <code>UsesTypeParams</code> accordingly for
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your field/variant.</p>
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</div></details><h2 id="structs" class="section-header"><a href="#structs">Structs</a></h2><ul class="item-table"><li><div class="item-name"><a class="struct" href="struct.Options.html" title="struct darling_core::usage::Options">Options</a></div><div class="desc docblock-short">Control struct for searching type parameters.</div></li></ul><h2 id="enums" class="section-header"><a href="#enums">Enums</a></h2><ul class="item-table"><li><div class="item-name"><a class="enum" href="enum.Purpose.html" title="enum darling_core::usage::Purpose">Purpose</a></div><div class="desc docblock-short">The goal of tracing generic parameter usage.</div></li></ul><h2 id="traits" class="section-header"><a href="#traits">Traits</a></h2><ul class="item-table"><li><div class="item-name"><a class="trait" href="trait.CollectLifetimes.html" title="trait darling_core::usage::CollectLifetimes">CollectLifetimes</a></div><div class="desc docblock-short">Searcher for finding lifetimes in an iterator.</div></li><li><div class="item-name"><a class="trait" href="trait.CollectTypeParams.html" title="trait darling_core::usage::CollectTypeParams">CollectTypeParams</a></div><div class="desc docblock-short">Searcher for finding type params in an iterator.</div></li><li><div class="item-name"><a class="trait" href="trait.GenericsExt.html" title="trait darling_core::usage::GenericsExt">GenericsExt</a></div><div class="desc docblock-short">Extension trait for pulling specific generics data from a generics AST representation.</div></li><li><div class="item-name"><a class="trait" href="trait.UsesLifetimes.html" title="trait darling_core::usage::UsesLifetimes">UsesLifetimes</a></div><div class="desc docblock-short">Searcher for finding lifetimes in a syntax tree.
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This can be used to determine which lifetimes must be emitted in generated code.</div></li><li><div class="item-name"><a class="trait" href="trait.UsesTypeParams.html" title="trait darling_core::usage::UsesTypeParams">UsesTypeParams</a></div><div class="desc docblock-short">Searcher for finding type params in a syntax tree.
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This can be used to determine if a given type parameter needs to be bounded in a generated impl.</div></li></ul><h2 id="types" class="section-header"><a href="#types">Type Aliases</a></h2><ul class="item-table"><li><div class="item-name"><a class="type" href="type.IdentRefSet.html" title="type darling_core::usage::IdentRefSet">IdentRefSet</a></div><div class="desc docblock-short">A set of references to idents.</div></li><li><div class="item-name"><a class="type" href="type.IdentSet.html" title="type darling_core::usage::IdentSet">IdentSet</a></div><div class="desc docblock-short">A set of idents.</div></li><li><div class="item-name"><a class="type" href="type.LifetimeRefSet.html" title="type darling_core::usage::LifetimeRefSet">LifetimeRefSet</a></div><div class="desc docblock-short">A set of references to lifetimes.</div></li><li><div class="item-name"><a class="type" href="type.LifetimeSet.html" title="type darling_core::usage::LifetimeSet">LifetimeSet</a></div><div class="desc docblock-short">A set of lifetimes.</div></li></ul></section></div></main></body></html> |