<!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 `/home/sangenya/.cargo/registry/src/github.com-1ecc6299db9ec823/scopeguard-1.1.0/src/lib.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>lib.rs - source</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled ><script id="default-settings"></script><script src="../../storage.js"></script><script src="../../crates.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../../favicon.svg">
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</pre><pre class="rust">
<span class="attribute">#![<span class="ident">cfg_attr</span>(<span class="ident">not</span>(<span class="ident">any</span>(<span class="ident">test</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)), <span class="ident">no_std</span>)]</span>
<span class="attribute">#![<span class="ident">doc</span>(<span class="ident">html_root_url</span> <span class="op">=</span> <span class="string">"https://docs.rs/scopeguard/1/"</span>)]</span>
<span class="doccomment">//! A scope guard will run a given closure when it goes out of scope,</span>
<span class="doccomment">//! even if the code between panics.</span>
<span class="doccomment">//! (as long as panic doesn't abort)</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Examples</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Hello World</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! This example creates a scope guard with an example function:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! extern crate scopeguard;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn f() {</span>
<span class="doccomment">//! let _guard = scopeguard::guard((), |_| {</span>
<span class="doccomment">//! println!("Hello Scope Exit!");</span>
<span class="doccomment">//! });</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // rest of the code here.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Here, at the end of `_guard`'s scope, the guard's closure is called.</span>
<span class="doccomment">//! // It is also called if we exit this scope through unwinding instead.</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! # fn main() {</span>
<span class="doccomment">//! # f();</span>
<span class="doccomment">//! # }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## `defer!`</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Use the `defer` macro to run an operation at scope exit,</span>
<span class="doccomment">//! either regular scope exit or during unwinding from a panic.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! #[macro_use(defer)] extern crate scopeguard;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! use std::cell::Cell;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn main() {</span>
<span class="doccomment">//! // use a cell to observe drops during and after the scope guard is active</span>
<span class="doccomment">//! let drop_counter = Cell::new(0);</span>
<span class="doccomment">//! {</span>
<span class="doccomment">//! // Create a scope guard using `defer!` for the current scope</span>
<span class="doccomment">//! defer! {</span>
<span class="doccomment">//! drop_counter.set(1 + drop_counter.get());</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Do regular operations here in the meantime.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Just before scope exit: it hasn't run yet.</span>
<span class="doccomment">//! assert_eq!(drop_counter.get(), 0);</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // The following scope end is where the defer closure is called</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! assert_eq!(drop_counter.get(), 1);</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Scope Guard with Value</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! If the scope guard closure needs to access an outer value that is also</span>
<span class="doccomment">//! mutated outside of the scope guard, then you may want to use the scope guard</span>
<span class="doccomment">//! with a value. The guard works like a smart pointer, so the inner value can</span>
<span class="doccomment">//! be accessed by reference or by mutable reference.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ### 1. The guard owns a file</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! In this example, the scope guard owns a file and ensures pending writes are</span>
<span class="doccomment">//! synced at scope exit.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! extern crate scopeguard;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! use std::fs::*;</span>
<span class="doccomment">//! use std::io::{self, Write};</span>
<span class="doccomment">//! # // Mock file so that we don't actually write a file</span>
<span class="doccomment">//! # struct MockFile;</span>
<span class="doccomment">//! # impl MockFile {</span>
<span class="doccomment">//! # fn create(_s: &str) -> io::Result<Self> { Ok(MockFile) }</span>
<span class="doccomment">//! # fn write_all(&self, _b: &[u8]) -> io::Result<()> { Ok(()) }</span>
<span class="doccomment">//! # fn sync_all(&self) -> io::Result<()> { Ok(()) }</span>
<span class="doccomment">//! # }</span>
<span class="doccomment">//! # use self::MockFile as File;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn try_main() -> io::Result<()> {</span>
<span class="doccomment">//! let f = File::create("newfile.txt")?;</span>
<span class="doccomment">//! let mut file = scopeguard::guard(f, |f| {</span>
<span class="doccomment">//! // ensure we flush file at return or panic</span>
<span class="doccomment">//! let _ = f.sync_all();</span>
<span class="doccomment">//! });</span>
<span class="doccomment">//! // Access the file through the scope guard itself</span>
<span class="doccomment">//! file.write_all(b"test me\n").map(|_| ())</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn main() {</span>
<span class="doccomment">//! try_main().unwrap();</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ### 2. The guard restores an invariant on scope exit</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! extern crate scopeguard;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! use std::mem::ManuallyDrop;</span>
<span class="doccomment">//! use std::ptr;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // This function, just for this example, takes the first element</span>
<span class="doccomment">//! // and inserts it into the assumed sorted tail of the vector.</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // For optimization purposes we temporarily violate an invariant of the</span>
<span class="doccomment">//! // Vec, that it owns all of its elements.</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // The safe approach is to use swap, which means two writes to memory,</span>
<span class="doccomment">//! // the optimization is to use a “hole” which uses only one write of memory</span>
<span class="doccomment">//! // for each position it moves.</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // We *must* use a scope guard to run this code safely. We</span>
<span class="doccomment">//! // are running arbitrary user code (comparison operators) that may panic.</span>
<span class="doccomment">//! // The scope guard ensures we restore the invariant after successful</span>
<span class="doccomment">//! // exit or during unwinding from panic.</span>
<span class="doccomment">//! fn insertion_sort_first<T>(v: &mut Vec<T>)</span>
<span class="doccomment">//! where T: PartialOrd</span>
<span class="doccomment">//! {</span>
<span class="doccomment">//! struct Hole<'a, T: 'a> {</span>
<span class="doccomment">//! v: &'a mut Vec<T>,</span>
<span class="doccomment">//! index: usize,</span>
<span class="doccomment">//! value: ManuallyDrop<T>,</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! unsafe {</span>
<span class="doccomment">//! // Create a moved-from location in the vector, a “hole”.</span>
<span class="doccomment">//! let value = ptr::read(&v[0]);</span>
<span class="doccomment">//! let mut hole = Hole { v: v, index: 0, value: ManuallyDrop::new(value) };</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Use a scope guard with a value.</span>
<span class="doccomment">//! // At scope exit, plug the hole so that the vector is fully</span>
<span class="doccomment">//! // initialized again.</span>
<span class="doccomment">//! // The scope guard owns the hole, but we can access it through the guard.</span>
<span class="doccomment">//! let mut hole_guard = scopeguard::guard(hole, |hole| {</span>
<span class="doccomment">//! // plug the hole in the vector with the value that was // taken out</span>
<span class="doccomment">//! let index = hole.index;</span>
<span class="doccomment">//! ptr::copy_nonoverlapping(&*hole.value, &mut hole.v[index], 1);</span>
<span class="doccomment">//! });</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // run algorithm that moves the hole in the vector here</span>
<span class="doccomment">//! // move the hole until it's in a sorted position</span>
<span class="doccomment">//! for i in 1..hole_guard.v.len() {</span>
<span class="doccomment">//! if *hole_guard.value >= hole_guard.v[i] {</span>
<span class="doccomment">//! // move the element back and the hole forward</span>
<span class="doccomment">//! let index = hole_guard.index;</span>
<span class="doccomment">//! ptr::copy_nonoverlapping(&hole_guard.v[index + 1], &mut hole_guard.v[index], 1);</span>
<span class="doccomment">//! hole_guard.index += 1;</span>
<span class="doccomment">//! } else {</span>
<span class="doccomment">//! break;</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // When the scope exits here, the Vec becomes whole again!</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn main() {</span>
<span class="doccomment">//! let string = String::from;</span>
<span class="doccomment">//! let mut data = vec![string("c"), string("a"), string("b"), string("d")];</span>
<span class="doccomment">//! insertion_sort_first(&mut data);</span>
<span class="doccomment">//! assert_eq!(data, vec!["a", "b", "c", "d"]);</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Crate Features</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! - `use_std`</span>
<span class="doccomment">//! + Enabled by default. Enables the `OnUnwind` and `OnSuccess` strategies.</span>
<span class="doccomment">//! + Disable to use `no_std`.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Rust Version</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! This version of the crate requires Rust 1.20 or later.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! The scopeguard 1.x release series will use a carefully considered version</span>
<span class="doccomment">//! upgrade policy, where in a later 1.x version, we will raise the minimum</span>
<span class="doccomment">//! required Rust version.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">any</span>(<span class="ident">test</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)))]</span>
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">core</span> <span class="kw">as</span> <span class="ident">std</span>;
<span class="kw">use</span> <span class="ident">std::fmt</span>;
<span class="kw">use</span> <span class="ident">std::marker::PhantomData</span>;
<span class="kw">use</span> <span class="ident">std::mem</span>::{<span class="self">self</span>, <span class="ident">ManuallyDrop</span>};
<span class="kw">use</span> <span class="ident">std::ops</span>::{<span class="ident">Deref</span>, <span class="ident">DerefMut</span>};
<span class="kw">use</span> <span class="ident">std::ptr</span>;
<span class="doccomment">/// Controls in which cases the associated code should be run</span>
<span class="kw">pub</span> <span class="kw">trait</span> <span class="ident">Strategy</span> {
<span class="doccomment">/// Return `true` if the guard’s associated code should run</span>
<span class="doccomment">/// (in the context where this method is called).</span>
<span class="kw">fn</span> <span class="ident">should_run</span>() <span class="op">-</span><span class="op">></span> <span class="ident">bool</span>;
}
<span class="doccomment">/// Always run on scope exit.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// “Always” run: on regular exit from a scope or on unwinding from a panic.</span>
<span class="doccomment">/// Can not run on abort, process exit, and other catastrophic events where</span>
<span class="doccomment">/// destructors don’t run.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Always</span> {}
<span class="doccomment">/// Run on scope exit through unwinding.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Requires crate feature `use_std`.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">OnUnwind</span> {}
<span class="doccomment">/// Run on regular scope exit, when not unwinding.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Requires crate feature `use_std`.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">OnSuccess</span> {}
<span class="kw">impl</span> <span class="ident">Strategy</span> <span class="kw">for</span> <span class="ident">Always</span> {
<span class="attribute">#[<span class="ident">inline</span>(<span class="ident">always</span>)]</span>
<span class="kw">fn</span> <span class="ident">should_run</span>() <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> { <span class="bool-val">true</span> }
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Strategy</span> <span class="kw">for</span> <span class="ident">OnUnwind</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">should_run</span>() <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> { <span class="ident">std::thread::panicking</span>() }
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Strategy</span> <span class="kw">for</span> <span class="ident">OnSuccess</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">should_run</span>() <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> { <span class="op">!</span><span class="ident">std::thread::panicking</span>() }
}
<span class="doccomment">/// Macro to create a `ScopeGuard` (always run).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The macro takes statements, which are the body of a closure</span>
<span class="doccomment">/// that will run when the scope is exited.</span>
<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="macro">macro_rules!</span> <span class="ident">defer</span> {
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">_guard</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="kw">crate</span><span class="macro-nonterminal">::guard</span>((), <span class="op">|</span>()<span class="op">|</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>)<span class="op">*</span> });
};
}
<span class="doccomment">/// Macro to create a `ScopeGuard` (run on successful scope exit).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The macro takes statements, which are the body of a closure</span>
<span class="doccomment">/// that will run when the scope is exited.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Requires crate feature `use_std`.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="macro">macro_rules!</span> <span class="ident">defer_on_success</span> {
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">_guard</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="kw">crate</span><span class="macro-nonterminal">::guard_on_success</span>((), <span class="op">|</span>()<span class="op">|</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>)<span class="op">*</span> });
};
}
<span class="doccomment">/// Macro to create a `ScopeGuard` (run on unwinding from panic).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The macro takes statements, which are the body of a closure</span>
<span class="doccomment">/// that will run when the scope is exited.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Requires crate feature `use_std`.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="macro">macro_rules!</span> <span class="ident">defer_on_unwind</span> {
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">_guard</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="kw">crate</span><span class="macro-nonterminal">::guard_on_unwind</span>((), <span class="op">|</span>()<span class="op">|</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>)<span class="op">*</span> });
};
}
<span class="doccomment">/// `ScopeGuard` is a scope guard that may own a protected value.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If you place a guard in a local variable, the closure can</span>
<span class="doccomment">/// run regardless how you leave the scope — through regular return or panic</span>
<span class="doccomment">/// (except if panic or other code aborts; so as long as destructors run).</span>
<span class="doccomment">/// It is run only once.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `S` parameter for [`Strategy`](trait.Strategy.html) determines if</span>
<span class="doccomment">/// the closure actually runs.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The guard's closure will be called with the held value in the destructor.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `ScopeGuard` implements `Deref` so that you can access the inner value.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span> <span class="op">=</span> <span class="ident">Always</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>),
<span class="ident">S</span>: <span class="ident">Strategy</span>,
{
<span class="ident">value</span>: <span class="ident">ManuallyDrop</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
<span class="ident">dropfn</span>: <span class="ident">ManuallyDrop</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>,
<span class="comment">// fn(S) -> S is used, so that the S is not taken into account for auto traits.</span>
<span class="ident">strategy</span>: <span class="ident">PhantomData</span><span class="op"><</span><span class="kw">fn</span>(<span class="ident">S</span>) <span class="op">-</span><span class="op">></span> <span class="ident">S</span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>),
<span class="ident">S</span>: <span class="ident">Strategy</span>,
{
<span class="doccomment">/// Create a `ScopeGuard` that owns `v` (accessible through deref) and calls</span>
<span class="doccomment">/// `dropfn` when its destructor runs.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `Strategy` decides whether the scope guard's closure should run.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">with_strategy</span>(<span class="ident">v</span>: <span class="ident">T</span>, <span class="ident">dropfn</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span> {
<span class="ident">ScopeGuard</span> {
<span class="ident">value</span>: <span class="ident">ManuallyDrop::new</span>(<span class="ident">v</span>),
<span class="ident">dropfn</span>: <span class="ident">ManuallyDrop::new</span>(<span class="ident">dropfn</span>),
<span class="ident">strategy</span>: <span class="ident">PhantomData</span>,
}
}
<span class="doccomment">/// “Defuse” the guard and extract the value without calling the closure.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// extern crate scopeguard;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// use scopeguard::{guard, ScopeGuard};</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn conditional() -> bool { true }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn main() {</span>
<span class="doccomment">/// let mut guard = guard(Vec::new(), |mut v| v.clear());</span>
<span class="doccomment">/// guard.push(1);</span>
<span class="doccomment">/// </span>
<span class="doccomment">/// if conditional() {</span>
<span class="doccomment">/// // a condition maybe makes us decide to</span>
<span class="doccomment">/// // “defuse” the guard and get back its inner parts</span>
<span class="doccomment">/// let value = ScopeGuard::into_inner(guard);</span>
<span class="doccomment">/// } else {</span>
<span class="doccomment">/// // guard still exists in this branch</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_inner</span>(<span class="ident">guard</span>: <span class="self">Self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">T</span> {
<span class="comment">// Cannot move out of Drop-implementing types, so</span>
<span class="comment">// ptr::read the value and forget the guard.</span>
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">value</span> <span class="op">=</span> <span class="ident">ptr::read</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">guard</span>.<span class="ident">value</span>);
<span class="comment">// read the closure so that it is dropped, and assign it to a local</span>
<span class="comment">// variable to ensure that it is only dropped after the guard has</span>
<span class="comment">// been forgotten. (In case the Drop impl of the closure, or that</span>
<span class="comment">// of any consumed captured variable, panics).</span>
<span class="kw">let</span> <span class="ident">_dropfn</span> <span class="op">=</span> <span class="ident">ptr::read</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">guard</span>.<span class="ident">dropfn</span>);
<span class="ident">mem::forget</span>(<span class="ident">guard</span>);
<span class="ident">value</span>
}
}
}
<span class="doccomment">/// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">guard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span><span class="op">></span>(<span class="ident">v</span>: <span class="ident">T</span>, <span class="ident">dropfn</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">Always</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>)
{
<span class="ident">ScopeGuard::with_strategy</span>(<span class="ident">v</span>, <span class="ident">dropfn</span>)
}
<span class="doccomment">/// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Requires crate feature `use_std`.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">guard_on_success</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span><span class="op">></span>(<span class="ident">v</span>: <span class="ident">T</span>, <span class="ident">dropfn</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">OnSuccess</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>)
{
<span class="ident">ScopeGuard::with_strategy</span>(<span class="ident">v</span>, <span class="ident">dropfn</span>)
}
<span class="doccomment">/// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Requires crate feature `use_std`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ## Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For performance reasons, or to emulate “only run guard on unwind” in</span>
<span class="doccomment">/// no-std environments, we can also use the default guard and simply manually</span>
<span class="doccomment">/// defuse it at the end of scope like the following example. (The performance</span>
<span class="doccomment">/// reason would be if the [`OnUnwind`]'s call to [std::thread::panicking()] is</span>
<span class="doccomment">/// an issue.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// extern crate scopeguard;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// use scopeguard::ScopeGuard;</span>
<span class="doccomment">/// # fn main() {</span>
<span class="doccomment">/// {</span>
<span class="doccomment">/// let guard = scopeguard::guard((), |_| {});</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // rest of the code here</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // we reached the end of scope without unwinding - defuse it</span>
<span class="doccomment">/// ScopeGuard::into_inner(guard);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">guard_on_unwind</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span><span class="op">></span>(<span class="ident">v</span>: <span class="ident">T</span>, <span class="ident">dropfn</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">OnUnwind</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>)
{
<span class="ident">ScopeGuard::with_strategy</span>(<span class="ident">v</span>, <span class="ident">dropfn</span>)
}
<span class="comment">// ScopeGuard can be Sync even if F isn't because the closure is</span>
<span class="comment">// not accessible from references.</span>
<span class="comment">// The guard does not store any instance of S, so it is also irrelevant.</span>
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Sync</span>,
<span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>),
<span class="ident">S</span>: <span class="ident">Strategy</span>
{}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>),
<span class="ident">S</span>: <span class="ident">Strategy</span>
{
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">T</span>;
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">T</span> {
<span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>),
<span class="ident">S</span>: <span class="ident">Strategy</span>
{
<span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span> {
<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>),
<span class="ident">S</span>: <span class="ident">Strategy</span>
{
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="comment">// This is OK because the fields are `ManuallyDrop`s</span>
<span class="comment">// which will not be dropped by the compiler.</span>
<span class="kw">let</span> (<span class="ident">value</span>, <span class="ident">dropfn</span>) <span class="op">=</span> <span class="kw">unsafe</span> {
(<span class="ident">ptr::read</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>), <span class="ident">ptr::read</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">dropfn</span>))
};
<span class="kw">if</span> <span class="ident">S::should_run</span>() {
<span class="ident">dropfn</span>(<span class="ident">value</span>);
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">ScopeGuard</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">F</span>, <span class="ident">S</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">fmt::Debug</span>,
<span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="ident">T</span>),
<span class="ident">S</span>: <span class="ident">Strategy</span>
{
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="macro">stringify!</span>(<span class="ident">ScopeGuard</span>))
.<span class="ident">field</span>(<span class="string">"value"</span>, <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>)
.<span class="ident">finish</span>()
}
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">tests</span> {
<span class="kw">use</span> <span class="kw">super</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">std::cell::Cell</span>;
<span class="kw">use</span> <span class="ident">std::panic::catch_unwind</span>;
<span class="kw">use</span> <span class="ident">std::panic::AssertUnwindSafe</span>;
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_defer</span>() {
<span class="kw">let</span> <span class="ident">drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
<span class="macro">defer!</span>(<span class="ident">drops</span>.<span class="ident">set</span>(<span class="number">1000</span>));
<span class="macro">assert_eq!</span>(<span class="ident">drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_defer_success_1</span>() {
<span class="kw">let</span> <span class="ident">drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
{
<span class="macro">defer_on_success!</span>(<span class="ident">drops</span>.<span class="ident">set</span>(<span class="number">1</span>));
<span class="macro">assert_eq!</span>(<span class="ident">drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
}
<span class="macro">assert_eq!</span>(<span class="ident">drops</span>.<span class="ident">get</span>(), <span class="number">1</span>);
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_defer_success_2</span>() {
<span class="kw">let</span> <span class="ident">drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">catch_unwind</span>(<span class="ident">AssertUnwindSafe</span>(<span class="op">|</span><span class="op">|</span> {
<span class="macro">defer_on_success!</span>(<span class="ident">drops</span>.<span class="ident">set</span>(<span class="number">1</span>));
<span class="macro">panic!</span>(<span class="string">"failure"</span>)
}));
<span class="macro">assert_eq!</span>(<span class="ident">drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_defer_unwind_1</span>() {
<span class="kw">let</span> <span class="ident">drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">catch_unwind</span>(<span class="ident">AssertUnwindSafe</span>(<span class="op">|</span><span class="op">|</span> {
<span class="macro">defer_on_unwind!</span>(<span class="ident">drops</span>.<span class="ident">set</span>(<span class="number">1</span>));
<span class="macro">assert_eq!</span>(<span class="ident">drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="macro">panic!</span>(<span class="string">"failure"</span>)
}));
<span class="macro">assert_eq!</span>(<span class="ident">drops</span>.<span class="ident">get</span>(), <span class="number">1</span>);
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_defer_unwind_2</span>() {
<span class="kw">let</span> <span class="ident">drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
{
<span class="macro">defer_on_unwind!</span>(<span class="ident">drops</span>.<span class="ident">set</span>(<span class="number">1</span>));
}
<span class="macro">assert_eq!</span>(<span class="ident">drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_only_dropped_by_closure_when_run</span>() {
<span class="kw">let</span> <span class="ident">value_drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="ident">value</span> <span class="op">=</span> <span class="ident">guard</span>((), <span class="op">|</span>()<span class="op">|</span> <span class="ident">value_drops</span>.<span class="ident">set</span>(<span class="number">1</span> <span class="op">+</span> <span class="ident">value_drops</span>.<span class="ident">get</span>()));
<span class="kw">let</span> <span class="ident">closure_drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">guard</span>(<span class="ident">value</span>, <span class="op">|</span><span class="kw">_</span><span class="op">|</span> <span class="ident">closure_drops</span>.<span class="ident">set</span>(<span class="number">1</span> <span class="op">+</span> <span class="ident">closure_drops</span>.<span class="ident">get</span>()));
<span class="macro">assert_eq!</span>(<span class="ident">value_drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="macro">assert_eq!</span>(<span class="ident">closure_drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="ident">drop</span>(<span class="ident">guard</span>);
<span class="macro">assert_eq!</span>(<span class="ident">value_drops</span>.<span class="ident">get</span>(), <span class="number">1</span>);
<span class="macro">assert_eq!</span>(<span class="ident">closure_drops</span>.<span class="ident">get</span>(), <span class="number">1</span>);
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_dropped_once_when_not_run</span>() {
<span class="kw">let</span> <span class="ident">value_drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="ident">value</span> <span class="op">=</span> <span class="ident">guard</span>((), <span class="op">|</span>()<span class="op">|</span> <span class="ident">value_drops</span>.<span class="ident">set</span>(<span class="number">1</span> <span class="op">+</span> <span class="ident">value_drops</span>.<span class="ident">get</span>()));
<span class="kw">let</span> <span class="ident">captured_drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="ident">captured</span> <span class="op">=</span> <span class="ident">guard</span>((), <span class="op">|</span>()<span class="op">|</span> <span class="ident">captured_drops</span>.<span class="ident">set</span>(<span class="number">1</span> <span class="op">+</span> <span class="ident">captured_drops</span>.<span class="ident">get</span>()));
<span class="kw">let</span> <span class="ident">closure_drops</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">guard_on_unwind</span>(<span class="ident">value</span>, <span class="op">|</span><span class="ident">value</span><span class="op">|</span> {
<span class="ident">drop</span>(<span class="ident">value</span>);
<span class="ident">drop</span>(<span class="ident">captured</span>);
<span class="ident">closure_drops</span>.<span class="ident">set</span>(<span class="number">1</span> <span class="op">+</span> <span class="ident">closure_drops</span>.<span class="ident">get</span>())
});
<span class="macro">assert_eq!</span>(<span class="ident">value_drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="macro">assert_eq!</span>(<span class="ident">captured_drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="macro">assert_eq!</span>(<span class="ident">closure_drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="ident">drop</span>(<span class="ident">guard</span>);
<span class="macro">assert_eq!</span>(<span class="ident">value_drops</span>.<span class="ident">get</span>(), <span class="number">1</span>);
<span class="macro">assert_eq!</span>(<span class="ident">captured_drops</span>.<span class="ident">get</span>(), <span class="number">1</span>);
<span class="macro">assert_eq!</span>(<span class="ident">closure_drops</span>.<span class="ident">get</span>(), <span class="number">0</span>);
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_into_inner</span>() {
<span class="kw">let</span> <span class="ident">dropped</span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="bool-val">false</span>);
<span class="kw">let</span> <span class="ident">value</span> <span class="op">=</span> <span class="ident">guard</span>(<span class="number">42</span>, <span class="op">|</span><span class="kw">_</span><span class="op">|</span> <span class="ident">dropped</span>.<span class="ident">set</span>(<span class="bool-val">true</span>));
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">guard</span>(<span class="ident">value</span>, <span class="op">|</span><span class="kw">_</span><span class="op">|</span> <span class="ident">dropped</span>.<span class="ident">set</span>(<span class="bool-val">true</span>));
<span class="kw">let</span> <span class="ident">inner</span> <span class="op">=</span> <span class="ident">ScopeGuard::into_inner</span>(<span class="ident">guard</span>);
<span class="macro">assert_eq!</span>(<span class="ident">dropped</span>.<span class="ident">get</span>(), <span class="bool-val">false</span>);
<span class="macro">assert_eq!</span>(<span class="kw-2">*</span><span class="ident">inner</span>, <span class="number">42</span>);
}
}
</pre></div>
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