43 lines
21 KiB
Plaintext
43 lines
21 KiB
Plaintext
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rust
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~R #rustc 1.93.0 (254b59607 2026-01-19)Á³VOÐêùÿ²?ÑL¼�§Ì± -a7a40eb546f9e2b0Á ë&Gf·Ã ¬ëñq:¤»b -bb76018b1173caf6Á‰ OnUnwindÁDÀ6 ¶<�6 use_stdÁLš6 œ�6 OnSuccessÁLà7 ¶<°7 ¢Lº7 œ°7 defer_on_successÁ„§? ¶<ô> ¢Lþ> œô> defer_on_unwindÁ|²B ¶<ÿA ¢L‰B œÿA guard_on_successÁ„”[ ¶<áZ ¢LëZ œáZ guard_on_unwindÁ|öb ¶<Ãb ¢LÍb œÃb testsÁ,¤n à$™n ³ “ StrategyÁ
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should_runÁ
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ð deferÁ
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ScopeGuardÁ ™ FÁ SÁ ˜ dropfnÁ strategyÁ ™ ° ¸
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with_strategyÁ
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into_innerÁ guardÁ ™ ° ™ ° ¸ $™ $° $¸ $š $‚ *™ *° *¸ *„ /™ /° /¸ /² 4™ 4° 4¸ 4Í AlwaysÁ :Í )
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3
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8
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8
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8
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;
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;
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;
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à` 9 i©©ìx ™ „ ˜ ˜ Ç Ô #Ze3ªáçç ™°¸ ì ½ ù ½ � ½ à`½ : 94
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9 $ * / à`#
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„ ì ù � 9³ “ Í0 Í Ü0 Á] PhantomDataÁ\ò0 ‰ ¯ Š ManuallyDropÁd�1 íÑ †,ª1 ì DerefMutÁD±1 ù ÷ Å1 ê
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Œ,±< ü ò… ¡ = @ p 8¹ lA O 7 https://docs.rs/scopeguard/1/Á üQ ü:8 ütE B A scope guard will run a given closure when it goes out of scope,Á üº$ ! even if the code between panics.Á üß$ ! (as long as panic doesn't abort)Á „ Ë tˆ # ExamplesÁ — Ë ”› ## Hello WorldÁ ® Ë ü²@ = This example creates a scope guard with an example function:Á ó Ë <÷ ```Á äÿ extern crate scopeguard;Á œ Ë d fn f() {Á ü0 - let _guard = scopeguard::guard((), |_| {Á üÞ* ' println!("Hello Scope Exit!");Á \‰ });Á • Ë ü™! // rest of the code here.Á » Ë ü¿O L // Here, at the end of `_guard`'s scope, the guard's closure is called.Á ü�M J // It is also called if we exit this scope through unwinding instead.Á ,Ý }Á Œã # fn main() {Á lõ
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# f();Á <ƒ # }Á <‹ û
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“ Ë |— ## `defer!`Á § Ë ü«< 9 Use the `defer` macro to run an operation at scope exit,Á üè? < either regular scope exit or during unwinding from a panic.Á ¨ Ë <¬ û
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ü´0 - #[macro_use(defer)] extern crate scopeguard;Á å Ë Äé use std::cell::Cell;Á ‚ Ë |† fn main() {Á ü–Q N // use a cell to observe drops during and after the scope guard is activeÁ üè( % let drop_counter = Cell::new(0);Á L‘ {Á ü› H E // Create a scope guard using `defer!` for the current scopeÁ ¤ä defer! {Á üù 9 6 drop_counter.set(1 + drop_counter.get());Á l³
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}Á Á
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Ë üÅ
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: 7 // Do regular operations here in the meantime.Á € Ë ü„ 9 6 // Just before scope exit: it hasn't run yet.Á ü¾ . + assert_eq!(drop_counter.get(), 0);Á í Ë üñ K H // The following scope end is where the defer closure is calledÁ L½ }Á üÇ * ' assert_eq!(drop_counter.get(), 1);Á ,ò º <ø û
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€
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Ë ì„
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## Scope Guard with ValueÁ ¢
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Ë ü¦
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J G If the scope guard closure needs to access an outer value that is alsoÁ üñ
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P M mutated outside of the scope guard, then you may want to use the scope guardÁ üÂN K with a value. The guard works like a smart pointer, so the inner value canÁ ü‘5 2 be accessed by reference or by mutable reference.Á Ç Ë üË ### 1. The guard owns a fileÁ ì Ë üðO L In this example, the scope guard owns a file and ensures pending writes areÁ ÌÀ synced at scope exit.Á Ú Ë <Þ û
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äæ Š ƒ Ë œ‡ use std::fs::*;Á ü› use std::io::{self, Write};Á ü»9 6 # // Mock file so that we don't actually write a fileÁ ´õ # struct MockFile;Á ¬Œ # impl MockFile {Á ü¢B ? # fn create(_s: &str) -> io::Result<Self> { Ok(MockFile) }Á üåE B # fn write_all(&self, _b: &[u8]) -> io::Result<()> { Ok(()) }Á ü«9 6 # fn sync_all(&self) -> io::Result<()> { Ok(()) }Á <å õ üí! # use self::MockFile as File;Á � Ë ü“% " fn try_main() -> io::Result<()> {Á ü¹- * let f = File::create("newfile.txt")?;Á üç1 . let mut file = scopeguard::guard(f, |f| {Á ü™6 3 // ensure we flush file at return or panicÁ üÐ! let _ = f.sync_all();Á \ò ¹ üþ9 6 // Access the file through the scope guard itselfÁ ü¸0 - file.write_all(b"test me\n").map(|_| ())Á ,é º ï Ë |ó Î äƒ try_main().unwrap();Á , º ¦ Ë <ª û
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² Ë ü¶8 5 ### 2. The guard restores an invariant on scope exitÁ ï Ë <ó û
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äû Š ˜ Ë üœ use std::mem::ManuallyDrop;Á Œ¼ use std::ptr;Á Î Ë üÒD A // This function, just for this example, takes the first elementÁ ü—A > // and inserts it into the assumed sorted tail of the vector.Á 4Ù //Á üàK H // For optimization purposes we temporarily violate an invariant of theÁ ü¬- * // Vec, that it owns all of its elements.Á 4Ú Ù) üáJ G // The safe approach is to use swap, which means two writes to memory,Á ü¬R O // the optimization is to use a “holeâ€� which uses only one write of memoryÁ üÿ" // for each position it moves.Á 4¢ Ù) ü© > ; // We *must* use a scope guard to run this code safely. WeÁ üè M J // are running arbitrary user code (comparison operators) that may panic.Á ü¶ H E // The scope guard ensures we restore the invariant after successfulÁ üÿ + ( // exit or during unwinding from panic.Á ü« . + fn insertion_sort_first<T>(v: &mut Vec<T>)Á ÜÚ where T: PartialOrdÁ ,ö {Á üü struct Hole<'a, T: 'a> {Á ô� v: &'a mut Vec<T>,Á ̼ index: usize,Á üÖ # value: ManuallyDrop<T>,Á Lú ö „ Ë „ˆ
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unsafe {Á ü™ H E // Create a moved-from location in the vector, a “holeâ€�.Á üâ ) & let value = ptr::read(&v[0]);Á üŒ!T Q let mut hole = Hole { v: v, index: 0, value: ManuallyDrop::new(value) };Á á! Ë üå!. + // Use a scope guard with a value.Á ü”"G D // At scope exit, plug the hole so that the vector is fullyÁ üÜ"! // initialized again.Á üþ"U R // The scope guard owns the hole, but we can access it through the guard.Á üÔ#A > let mut hole_guard = scopeguard::guard(hole, |hole| {Á ü–$S P // plug the hole in the vector with the value that was // taken outÁ üê$' $ let index = hole.index;Á ü’%N K ptr::copy_nonoverlapping(&*hole.value, &mut hole.v[index],
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ù ÷ 0 ê
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ŒC ĸ0 ŒD×0 žÄå0 ¼´ƒ1 îÜŸ1 DÀ1 0”‰2 üË1= : Controls in which cases the associated code should be runÁ D“2 ªâ ü‰2« æG æG Äš3 ü¢2= : Return `true` if the guard’s associated code should runÁ üä21 . (in the context where this method is called).ÁT�3
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îGÄî7 ™ ¼£8 T¦8
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”¤< üó:0 - Macro to create a `ScopeGuard` (always run).Á ¤; Ë ü¨;? < The macro takes statements, which are the body of a closureÁ üè;+ ( that will run when the scope is exited.Á &|”< C ·< Ž= ½< Ç< , ¾< ¿< Å< , À< 8 tÁ Á< & Â< 8� Ã<
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Æ< *É< Ì< ‹= 8 Ö< 8 _guardÁ 4Ú< á< , ã< 8 ,ä< 'é< 8¡ ,ë< ð< „= ñ< ò< $ ó< õ< ö< ÷< ø< ú< ƒ= , ü< ý< €= , þ< 8œK ÿ<
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