| <!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/lazy_static-1.4.0/src/lib.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>lib.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="../../lazy_static/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="../../lazy_static/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="comment">// Copyright 2016 lazy-static.rs Developers |
| // |
| // Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or |
| // http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or |
| // http://opensource.org/licenses/MIT>, at your option. This file may not be |
| // copied, modified, or distributed except according to those terms. |
| |
| </span><span class="doccomment">/*! |
| A macro for declaring lazily evaluated statics. |
| |
| Using this macro, it is possible to have `static`s that require code to be |
| executed at runtime in order to be initialized. |
| This includes anything requiring heap allocations, like vectors or hash maps, |
| as well as anything that requires function calls to be computed. |
| |
| # Syntax |
| |
| ```ignore |
| lazy_static! { |
| [pub] static ref NAME_1: TYPE_1 = EXPR_1; |
| [pub] static ref NAME_2: TYPE_2 = EXPR_2; |
| ... |
| [pub] static ref NAME_N: TYPE_N = EXPR_N; |
| } |
| ``` |
| |
| Attributes (including doc comments) are supported as well: |
| |
| ```rust |
| # #[macro_use] |
| # extern crate lazy_static; |
| # fn main() { |
| lazy_static! { |
| /// This is an example for using doc comment attributes |
| static ref EXAMPLE: u8 = 42; |
| } |
| # } |
| ``` |
| |
| # Semantics |
| |
| For a given `static ref NAME: TYPE = EXPR;`, the macro generates a unique type that |
| implements `Deref<TYPE>` and stores it in a static with name `NAME`. (Attributes end up |
| attaching to this type.) |
| |
| On first deref, `EXPR` gets evaluated and stored internally, such that all further derefs |
| can return a reference to the same object. Note that this can lead to deadlocks |
| if you have multiple lazy statics that depend on each other in their initialization. |
| |
| Apart from the lazy initialization, the resulting "static ref" variables |
| have generally the same properties as regular "static" variables: |
| |
| - Any type in them needs to fulfill the `Sync` trait. |
| - If the type has a destructor, then it will not run when the process exits. |
| |
| # Example |
| |
| Using the macro: |
| |
| ```rust |
| #[macro_use] |
| extern crate lazy_static; |
| |
| use std::collections::HashMap; |
| |
| lazy_static! { |
| static ref HASHMAP: HashMap<u32, &'static str> = { |
| let mut m = HashMap::new(); |
| m.insert(0, "foo"); |
| m.insert(1, "bar"); |
| m.insert(2, "baz"); |
| m |
| }; |
| static ref COUNT: usize = HASHMAP.len(); |
| static ref NUMBER: u32 = times_two(21); |
| } |
| |
| fn times_two(n: u32) -> u32 { n * 2 } |
| |
| fn main() { |
| println!("The map has {} entries.", *COUNT); |
| println!("The entry for `0` is \"{}\".", HASHMAP.get(&0).unwrap()); |
| println!("A expensive calculation on a static results in: {}.", *NUMBER); |
| } |
| ``` |
| |
| # Implementation details |
| |
| The `Deref` implementation uses a hidden static variable that is guarded by an atomic check on each access. |
| |
| # Cargo features |
| |
| This crate provides one cargo feature: |
| |
| - `spin_no_std`: This allows using this crate in a no-std environment, by depending on the standalone `spin` crate. |
| |
| */ |
| |
| </span><span class="attribute">#![doc(html_root_url = <span class="string">"https://docs.rs/lazy_static/1.4.0"</span>)] |
| #![no_std] |
| |
| #[cfg(not(feature = <span class="string">"spin_no_std"</span>))] |
| #[path=<span class="string">"inline_lazy.rs"</span>] |
| #[doc(hidden)] |
| </span><span class="kw">pub mod </span>lazy; |
| |
| <span class="attribute">#[cfg(test)] |
| #[macro_use] |
| </span><span class="kw">extern crate </span>doc_comment; |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="macro">doctest!</span>(<span class="string">"../README.md"</span>); |
| |
| <span class="attribute">#[cfg(feature = <span class="string">"spin_no_std"</span>)] |
| #[path=<span class="string">"core_lazy.rs"</span>] |
| #[doc(hidden)] |
| </span><span class="kw">pub mod </span>lazy; |
| |
| <span class="attribute">#[doc(hidden)] |
| </span><span class="kw">pub use </span>core::ops::Deref <span class="kw">as </span>__Deref; |
| |
| <span class="attribute">#[macro_export(local_inner_macros)] |
| #[doc(hidden)] |
| </span><span class="macro">macro_rules! </span>__lazy_static_internal { |
| <span class="comment">// optional visibility restrictions are wrapped in `()` to allow for |
| // explicitly passing otherwise implicit information about private items |
| </span>($(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>:meta]</span>)* ($(<span class="macro-nonterminal">$vis</span>:tt)<span class="kw-2">*</span>) <span class="kw">static </span><span class="kw-2">ref </span><span class="macro-nonterminal">$N</span>:ident : <span class="macro-nonterminal">$T</span>:ty = <span class="macro-nonterminal">$e</span>:expr; $(<span class="macro-nonterminal">$t</span>:tt)<span class="kw-2">*</span>) => { |
| <span class="macro">__lazy_static_internal!</span>(@MAKE TY, $(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>]</span>)<span class="kw-2">*</span>, ($(<span class="macro-nonterminal">$vis</span>)<span class="kw-2">*</span>), <span class="macro-nonterminal">$N</span>); |
| <span class="macro">__lazy_static_internal!</span>(@TAIL, <span class="macro-nonterminal">$N </span>: <span class="macro-nonterminal">$T </span>= <span class="macro-nonterminal">$e</span>); |
| <span class="macro">lazy_static!</span>($(<span class="macro-nonterminal">$t</span>)<span class="kw-2">*</span>); |
| }; |
| (@TAIL, <span class="macro-nonterminal">$N</span>:ident : <span class="macro-nonterminal">$T</span>:ty = <span class="macro-nonterminal">$e</span>:expr) => { |
| <span class="kw">impl </span><span class="macro-nonterminal">$crate::__Deref </span><span class="kw">for </span><span class="macro-nonterminal">$N </span>{ |
| <span class="kw">type </span>Target = <span class="macro-nonterminal">$T</span>; |
| <span class="kw">fn </span>deref(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span><span class="macro-nonterminal">$T </span>{ |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>__static_ref_initialize() -> <span class="macro-nonterminal">$T </span>{ <span class="macro-nonterminal">$e </span>} |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>__stability() -> <span class="kw-2">&</span><span class="lifetime">'static </span><span class="macro-nonterminal">$T </span>{ |
| <span class="macro">__lazy_static_create!</span>(LAZY, <span class="macro-nonterminal">$T</span>); |
| LAZY.get(__static_ref_initialize) |
| } |
| __stability() |
| } |
| } |
| <span class="kw">impl </span><span class="macro-nonterminal">$crate::LazyStatic </span><span class="kw">for </span><span class="macro-nonterminal">$N </span>{ |
| <span class="kw">fn </span>initialize(lazy: <span class="kw-2">&</span><span class="self">Self</span>) { |
| <span class="kw">let _ </span>= <span class="kw-2">&**</span>lazy; |
| } |
| } |
| }; |
| <span class="comment">// `vis` is wrapped in `()` to prevent parsing ambiguity |
| </span>(@MAKE TY, $(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>:meta]</span>)<span class="kw-2">*</span>, ($(<span class="macro-nonterminal">$vis</span>:tt)<span class="kw-2">*</span>), <span class="macro-nonterminal">$N</span>:ident) => { |
| <span class="attribute">#[allow(missing_copy_implementations)] |
| #[allow(non_camel_case_types)] |
| #[allow(dead_code)] |
| </span>$(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>]</span>)* |
| $(<span class="macro-nonterminal">$vis</span>)* <span class="kw">struct </span><span class="macro-nonterminal">$N </span>{__private_field: ()} |
| <span class="attribute">#[doc(hidden)] |
| </span>$(<span class="macro-nonterminal">$vis</span>)* <span class="kw">static </span><span class="macro-nonterminal">$N</span>: <span class="macro-nonterminal">$N </span>= <span class="macro-nonterminal">$N </span>{__private_field: ()}; |
| }; |
| () => () |
| } |
| |
| <span class="attribute">#[macro_export(local_inner_macros)] |
| </span><span class="macro">macro_rules! </span>lazy_static { |
| ($(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>:meta]</span>)* <span class="kw">static </span><span class="kw-2">ref </span><span class="macro-nonterminal">$N</span>:ident : <span class="macro-nonterminal">$T</span>:ty = <span class="macro-nonterminal">$e</span>:expr; $(<span class="macro-nonterminal">$t</span>:tt)<span class="kw-2">*</span>) => { |
| <span class="comment">// use `()` to explicitly forward the information about private items |
| </span><span class="macro">__lazy_static_internal!</span>($(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>]</span>)* () <span class="kw">static </span><span class="kw-2">ref </span><span class="macro-nonterminal">$N </span>: <span class="macro-nonterminal">$T </span>= <span class="macro-nonterminal">$e</span>; $(<span class="macro-nonterminal">$t</span>)<span class="kw-2">*</span>); |
| }; |
| ($(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>:meta]</span>)* <span class="kw">pub static </span><span class="kw-2">ref </span><span class="macro-nonterminal">$N</span>:ident : <span class="macro-nonterminal">$T</span>:ty = <span class="macro-nonterminal">$e</span>:expr; $(<span class="macro-nonterminal">$t</span>:tt)<span class="kw-2">*</span>) => { |
| <span class="macro">__lazy_static_internal!</span>($(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>]</span>)* (<span class="kw">pub</span>) <span class="kw">static </span><span class="kw-2">ref </span><span class="macro-nonterminal">$N </span>: <span class="macro-nonterminal">$T </span>= <span class="macro-nonterminal">$e</span>; $(<span class="macro-nonterminal">$t</span>)<span class="kw-2">*</span>); |
| }; |
| ($(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>:meta]</span>)* <span class="kw">pub </span>($(<span class="macro-nonterminal">$vis</span>:tt)+) <span class="kw">static </span><span class="kw-2">ref </span><span class="macro-nonterminal">$N</span>:ident : <span class="macro-nonterminal">$T</span>:ty = <span class="macro-nonterminal">$e</span>:expr; $(<span class="macro-nonterminal">$t</span>:tt)<span class="kw-2">*</span>) => { |
| <span class="macro">__lazy_static_internal!</span>($(<span class="attribute">#[<span class="macro-nonterminal">$attr</span>]</span>)* (<span class="kw">pub </span>($(<span class="macro-nonterminal">$vis</span>)+)) <span class="kw">static </span><span class="kw-2">ref </span><span class="macro-nonterminal">$N </span>: <span class="macro-nonterminal">$T </span>= <span class="macro-nonterminal">$e</span>; $(<span class="macro-nonterminal">$t</span>)<span class="kw-2">*</span>); |
| }; |
| () => () |
| } |
| |
| <span class="doccomment">/// Support trait for enabling a few common operation on lazy static values. |
| /// |
| /// This is implemented by each defined lazy static, and |
| /// used by the free functions in this crate. |
| </span><span class="kw">pub trait </span>LazyStatic { |
| <span class="attribute">#[doc(hidden)] |
| </span><span class="kw">fn </span>initialize(lazy: <span class="kw-2">&</span><span class="self">Self</span>); |
| } |
| |
| <span class="doccomment">/// Takes a shared reference to a lazy static and initializes |
| /// it if it has not been already. |
| /// |
| /// This can be used to control the initialization point of a lazy static. |
| /// |
| /// Example: |
| /// |
| /// ```rust |
| /// #[macro_use] |
| /// extern crate lazy_static; |
| /// |
| /// lazy_static! { |
| /// static ref BUFFER: Vec<u8> = (0..255).collect(); |
| /// } |
| /// |
| /// fn main() { |
| /// lazy_static::initialize(&BUFFER); |
| /// |
| /// // ... |
| /// work_with_initialized_data(&BUFFER); |
| /// } |
| /// # fn work_with_initialized_data(_: &[u8]) {} |
| /// ``` |
| </span><span class="kw">pub fn </span>initialize<T: LazyStatic>(lazy: <span class="kw-2">&</span>T) { |
| LazyStatic::initialize(lazy); |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="lazy_static" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
