| <!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="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/ghost-0.1.9/src/variance.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>variance.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="../../source-script.js"></script><script defer src="../../source-files.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../ghost/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../ghost/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="kw">use </span>proc_macro2::{Ident, TokenStream}; |
| <span class="kw">use </span>quote::quote; |
| <span class="kw">use </span>syn::{Attribute, LifetimeParam, Meta, TypeParam}; |
| |
| <span class="kw">enum </span>Variance { |
| Covariant, |
| Contravariant, |
| Invariant, |
| } |
| |
| <span class="kw">pub trait </span>HasVarianceAttribute { |
| <span class="kw">fn </span>attrs(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="kw-2">&mut </span>Vec<Attribute>; |
| } |
| |
| <span class="kw">impl </span>HasVarianceAttribute <span class="kw">for </span>TypeParam { |
| <span class="kw">fn </span>attrs(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="kw-2">&mut </span>Vec<Attribute> { |
| <span class="kw-2">&mut </span><span class="self">self</span>.attrs |
| } |
| } |
| |
| <span class="kw">impl </span>HasVarianceAttribute <span class="kw">for </span>LifetimeParam { |
| <span class="kw">fn </span>attrs(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="kw-2">&mut </span>Vec<Attribute> { |
| <span class="kw-2">&mut </span><span class="self">self</span>.attrs |
| } |
| } |
| |
| <span class="kw">pub fn </span>apply( |
| param: <span class="kw-2">&mut </span><span class="kw">dyn </span>HasVarianceAttribute, |
| base: TokenStream, |
| type_param: <span class="kw-2">&</span>Ident, |
| ) -> TokenStream { |
| <span class="kw">let </span><span class="kw-2">mut </span>variance = Variance::Covariant; |
| |
| <span class="kw">let </span>attrs = param.attrs(); |
| <span class="kw-2">*</span>attrs = attrs |
| .drain(..) |
| .filter(|attr| { |
| <span class="kw">if let </span>Meta::Path(attr_path) = <span class="kw-2">&</span>attr.meta { |
| <span class="kw">if </span>attr_path.is_ident(<span class="string">"contra"</span>) { |
| variance = Variance::Contravariant; |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } <span class="kw">else if </span>attr_path.is_ident(<span class="string">"invariant"</span>) { |
| variance = Variance::Invariant; |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| } |
| <span class="bool-val">true |
| </span>}) |
| .collect(); |
| |
| <span class="kw">let </span>phantom = <span class="macro">quote!</span>(<span class="self">self</span>::#type_param<#base>); |
| <span class="kw">match </span>variance { |
| Variance::Covariant => base, |
| Variance::Contravariant => <span class="macro">quote!</span>(<span class="kw">fn</span>(#phantom)), |
| Variance::Invariant => <span class="macro">quote!</span>(<span class="kw">fn</span>(#phantom) -> #phantom), |
| } |
| } |
| </code></pre></div> |
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