# lib.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/scopeguard-1.1.0/src/lib.rs`.
Keywords: rust, rustlang, rust-lang

      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318
    319
    320
    321
    322
    323
    324
    325
    326
    327
    328
    329
    330
    331
    332
    333
    334
    335
    336
    337
    338
    339
    340
    341
    342
    343
    344
    345
    346
    347
    348
    349
    350
    351
    352
    353
    354
    355
    356
    357
    358
    359
    360
    361
    362
    363
    364
    365
    366
    367
    368
    369
    370
    371
    372
    373
    374
    375
    376
    377
    378
    379
    380
    381
    382
    383
    384
    385
    386
    387
    388
    389
    390
    391
    392
    393
    394
    395
    396
    397
    398
    399
    400
    401
    402
    403
    404
    405
    406
    407
    408
    409
    410
    411
    412
    413
    414
    415
    416
    417
    418
    419
    420
    421
    422
    423
    424
    425
    426
    427
    428
    429
    430
    431
    432
    433
    434
    435
    436
    437
    438
    439
    440
    441
    442
    443
    444
    445
    446
    447
    448
    449
    450
    451
    452
    453
    454
    455
    456
    457
    458
    459
    460
    461
    462
    463
    464
    465
    466
    467
    468
    469
    470
    471
    472
    473
    474
    475
    476
    477
    478
    479
    480
    481
    482
    483
    484
    485
    486
    487
    488
    489
    490
    491
    492
    493
    494
    495
    496
    497
    498
    499
    500
    501
    502
    503
    504
    505
    506
    507
    508
    509
    510
    511
    512
    513
    514
    515
    516
    517
    518
    519
    520
    521
    522
    523
    524
    525
    526
    527
    528
    529
    530
    531
    532
    533
    534
    535
    536
    537
    538
    539
    540
    541
    542
    543
    544
    545
    546
    547
    548
    549
    550
    551
    552
    553
    554
    555
    556
    557
    558
    559
    560
    561
    562
    563
    564
    565
    566
    567
    568
    569
    570
    571
    572
    573
    574
    575
    576
    577
    578

    #![cfg_attr(not(any(test, feature = "use_std")), no_std)]
    #![doc(html_root_url = "https://docs.rs/scopeguard/1/")]

    //! A scope guard will run a given closure when it goes out of scope,
    //! even if the code between panics.
    //! (as long as panic doesn't abort)
    //!
    //! # Examples
    //!
    //! ## Hello World
    //!
    //! This example creates a scope guard with an example function:
    //!
    //! ```
    //! extern crate scopeguard;
    //!
    //! fn f() {
    //!     let _guard = scopeguard::guard((), |_| {
    //!         println!("Hello Scope Exit!");
    //!     });
    //!
    //!     // rest of the code here.
    //!
    //!     // Here, at the end of `_guard`'s scope, the guard's closure is called.
    //!     // It is also called if we exit this scope through unwinding instead.
    //! }
    //! # fn main() {
    //! #    f();
    //! # }
    //! ```
    //!
    //! ## `defer!`
    //!
    //! Use the `defer` macro to run an operation at scope exit,
    //! either regular scope exit or during unwinding from a panic.
    //!
    //! ```
    //! #[macro_use(defer)] extern crate scopeguard;
    //!
    //! use std::cell::Cell;
    //!
    //! fn main() {
    //!     // use a cell to observe drops during and after the scope guard is active
    //!     let drop_counter = Cell::new(0);
    //!     {
    //!         // Create a scope guard using `defer!` for the current scope
    //!         defer! {
    //!             drop_counter.set(1 + drop_counter.get());
    //!         }
    //!
    //!         // Do regular operations here in the meantime.
    //!
    //!         // Just before scope exit: it hasn't run yet.
    //!         assert_eq!(drop_counter.get(), 0);
    //!
    //!         // The following scope end is where the defer closure is called
    //!     }
    //!     assert_eq!(drop_counter.get(), 1);
    //! }
    //! ```
    //!
    //! ## Scope Guard with Value
    //!
    //! If the scope guard closure needs to access an outer value that is also
    //! mutated outside of the scope guard, then you may want to use the scope guard
    //! with a value. The guard works like a smart pointer, so the inner value can
    //! be accessed by reference or by mutable reference.
    //!
    //! ### 1. The guard owns a file
    //!
    //! In this example, the scope guard owns a file and ensures pending writes are
    //! synced at scope exit.
    //!
    //! ```
    //! extern crate scopeguard;
    //!
    //! use std::fs::*;
    //! use std::io::{self, Write};
    //! # // Mock file so that we don't actually write a file
    //! # struct MockFile;
    //! # impl MockFile {
    //! #     fn create(_s: &str) -> io::Result<Self> { Ok(MockFile) }
    //! #     fn write_all(&self, _b: &[u8]) -> io::Result<()> { Ok(()) }
    //! #     fn sync_all(&self) -> io::Result<()> { Ok(()) }
    //! # }
    //! # use self::MockFile as File;
    //!
    //! fn try_main() -> io::Result<()> {
    //!     let f = File::create("newfile.txt")?;
    //!     let mut file = scopeguard::guard(f, |f| {
    //!         // ensure we flush file at return or panic
    //!         let _ = f.sync_all();
    //!     });
    //!     // Access the file through the scope guard itself
    //!     file.write_all(b"test me\n").map(|_| ())
    //! }
    //!
    //! fn main() {
    //!     try_main().unwrap();
    //! }
    //!
    //! ```
    //!
    //! ### 2. The guard restores an invariant on scope exit
    //!
    //! ```
    //! extern crate scopeguard;
    //!
    //! use std::mem::ManuallyDrop;
    //! use std::ptr;
    //!
    //! // This function, just for this example, takes the first element
    //! // and inserts it into the assumed sorted tail of the vector.
    //! //
    //! // For optimization purposes we temporarily violate an invariant of the
    //! // Vec, that it owns all of its elements.
    //! //
    //! // The safe approach is to use swap, which means two writes to memory,
    //! // the optimization is to use a “hole” which uses only one write of memory
    //! // for each position it moves.
    //! //
    //! // We *must* use a scope guard to run this code safely. We
    //! // are running arbitrary user code (comparison operators) that may panic.
    //! // The scope guard ensures we restore the invariant after successful
    //! // exit or during unwinding from panic.
    //! fn insertion_sort_first<T>(v: &mut Vec<T>)
    //!     where T: PartialOrd
    //! {
    //!     struct Hole<'a, T: 'a> {
    //!         v: &'a mut Vec<T>,
    //!         index: usize,
    //!         value: ManuallyDrop<T>,
    //!     }
    //!
    //!     unsafe {
    //!         // Create a moved-from location in the vector, a “hole”.
    //!         let value = ptr::read(&v[0]);
    //!         let mut hole = Hole { v: v, index: 0, value: ManuallyDrop::new(value) };
    //!
    //!         // Use a scope guard with a value.
    //!         // At scope exit, plug the hole so that the vector is fully
    //!         // initialized again.
    //!         // The scope guard owns the hole, but we can access it through the guard.
    //!         let mut hole_guard = scopeguard::guard(hole, |hole| {
    //!             // plug the hole in the vector with the value that was // taken out
    //!             let index = hole.index;
    //!             ptr::copy_nonoverlapping(&*hole.value, &mut hole.v[index], 1);
    //!         });
    //!
    //!         // run algorithm that moves the hole in the vector here
    //!         // move the hole until it's in a sorted position
    //!         for i in 1..hole_guard.v.len() {
    //!             if *hole_guard.value >= hole_guard.v[i] {
    //!                 // move the element back and the hole forward
    //!                 let index = hole_guard.index;
    //!                 ptr::copy_nonoverlapping(&hole_guard.v[index + 1], &mut hole_guard.v[index], 1);
    //!                 hole_guard.index += 1;
    //!             } else {
    //!                 break;
    //!             }
    //!         }
    //!
    //!         // When the scope exits here, the Vec becomes whole again!
    //!     }
    //! }
    //!
    //! fn main() {
    //!     let string = String::from;
    //!     let mut data = vec![string("c"), string("a"), string("b"), string("d")];
    //!     insertion_sort_first(&mut data);
    //!     assert_eq!(data, vec!["a", "b", "c", "d"]);
    //! }
    //!
    //! ```
    //!
    //!
    //! # Crate Features
    //!
    //! - `use_std`
    //!   + Enabled by default. Enables the `OnUnwind` and `OnSuccess` strategies.
    //!   + Disable to use `no_std`.
    //!
    //! # Rust Version
    //!
    //! This version of the crate requires Rust 1.20 or later.
    //!
    //! The scopeguard 1.x release series will use a carefully considered version
    //! upgrade policy, where in a later 1.x version, we will raise the minimum
    //! required Rust version.

    #[cfg(not(any(test, feature = "use_std")))]
    extern crate core as std;

    use std::fmt;
    use std::marker::PhantomData;
    use std::mem::{self, ManuallyDrop};
    use std::ops::{Deref, DerefMut};
    use std::ptr;

    /// Controls in which cases the associated code should be run
    pub trait Strategy {
        /// Return `true` if the guard’s associated code should run
        /// (in the context where this method is called).
        fn should_run() -> bool;
    }

    /// Always run on scope exit.
    ///
    /// “Always” run: on regular exit from a scope or on unwinding from a panic.
    /// Can not run on abort, process exit, and other catastrophic events where
    /// destructors don’t run.
    #[derive(Debug)]
    pub enum Always {}

    /// Run on scope exit through unwinding.
    ///
    /// Requires crate feature `use_std`.
    #[cfg(feature = "use_std")]
    #[derive(Debug)]
    pub enum OnUnwind {}

    /// Run on regular scope exit, when not unwinding.
    ///
    /// Requires crate feature `use_std`.
    #[cfg(feature = "use_std")]
    #[derive(Debug)]
    pub enum OnSuccess {}

    impl Strategy for Always {
        #[inline(always)]
        fn should_run() -> bool { true }
    }

    #[cfg(feature = "use_std")]
    impl Strategy for OnUnwind {
        #[inline]
        fn should_run() -> bool { std::thread::panicking() }
    }

    #[cfg(feature = "use_std")]
    impl Strategy for OnSuccess {
        #[inline]
        fn should_run() -> bool { !std::thread::panicking() }
    }

    /// Macro to create a `ScopeGuard` (always run).
    ///
    /// The macro takes statements, which are the body of a closure
    /// that will run when the scope is exited.
    #[macro_export]
    macro_rules! defer {
        ($($t:tt)*) => {
            let _guard = $crate::guard((), |()| { $($t)* });
        };
    }

    /// Macro to create a `ScopeGuard` (run on successful scope exit).
    ///
    /// The macro takes statements, which are the body of a closure
    /// that will run when the scope is exited.
    ///
    /// Requires crate feature `use_std`.
    #[cfg(feature = "use_std")]
    #[macro_export]
    macro_rules! defer_on_success {
        ($($t:tt)*) => {
            let _guard = $crate::guard_on_success((), |()| { $($t)* });
        };
    }

    /// Macro to create a `ScopeGuard` (run on unwinding from panic).
    ///
    /// The macro takes statements, which are the body of a closure
    /// that will run when the scope is exited.
    ///
    /// Requires crate feature `use_std`.
    #[cfg(feature = "use_std")]
    #[macro_export]
    macro_rules! defer_on_unwind {
        ($($t:tt)*) => {
            let _guard = $crate::guard_on_unwind((), |()| { $($t)* });
        };
    }

    /// `ScopeGuard` is a scope guard that may own a protected value.
    ///
    /// If you place a guard in a local variable, the closure can
    /// run regardless how you leave the scope — through regular return or panic
    /// (except if panic or other code aborts; so as long as destructors run).
    /// It is run only once.
    ///
    /// The `S` parameter for [`Strategy`](trait.Strategy.html) determines if
    /// the closure actually runs.
    ///
    /// The guard's closure will be called with the held value in the destructor.
    ///
    /// The `ScopeGuard` implements `Deref` so that you can access the inner value.
    pub struct ScopeGuard<T, F, S = Always>
        where F: FnOnce(T),
              S: Strategy,
    {
        value: ManuallyDrop<T>,
        dropfn: ManuallyDrop<F>,
        // fn(S) -> S is used, so that the S is not taken into account for auto traits.
        strategy: PhantomData<fn(S) -> S>,
    }

    impl<T, F, S> ScopeGuard<T, F, S>
        where F: FnOnce(T),
              S: Strategy,
    {
        /// Create a `ScopeGuard` that owns `v` (accessible through deref) and calls
        /// `dropfn` when its destructor runs.
        ///
        /// The `Strategy` decides whether the scope guard's closure should run.
        #[inline]
        pub fn with_strategy(v: T, dropfn: F) -> ScopeGuard<T, F, S> {
            ScopeGuard {
                value: ManuallyDrop::new(v),
                dropfn: ManuallyDrop::new(dropfn),
                strategy: PhantomData,
            }
        }

        /// “Defuse” the guard and extract the value without calling the closure.
        ///
        /// ```
        /// extern crate scopeguard;
        ///
        /// use scopeguard::{guard, ScopeGuard};
        ///
        /// fn conditional() -> bool { true }
        ///
        /// fn main() {
        ///     let mut guard = guard(Vec::new(), |mut v| v.clear());
        ///     guard.push(1);
        ///
        ///     if conditional() {
        ///         // a condition maybe makes us decide to
        ///         // “defuse” the guard and get back its inner parts
        ///         let value = ScopeGuard::into_inner(guard);
        ///     } else {
        ///         // guard still exists in this branch
        ///     }
        /// }
        /// ```
        #[inline]
        pub fn into_inner(guard: Self) -> T {
            // Cannot move out of Drop-implementing types, so
            // ptr::read the value and forget the guard.
            unsafe {
                let value = ptr::read(&*guard.value);
                // read the closure so that it is dropped, and assign it to a local
                // variable to ensure that it is only dropped after the guard has
                // been forgotten. (In case the Drop impl of the closure, or that
                // of any consumed captured variable, panics).
                let _dropfn = ptr::read(&*guard.dropfn);
                mem::forget(guard);
                value
            }
        }
    }

    /// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.
    #[inline]
    pub fn guard<T, F>(v: T, dropfn: F) -> ScopeGuard<T, F, Always>
        where F: FnOnce(T)
    {
        ScopeGuard::with_strategy(v, dropfn)
    }

    /// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.
    ///
    /// Requires crate feature `use_std`.
    #[cfg(feature = "use_std")]
    #[inline]
    pub fn guard_on_success<T, F>(v: T, dropfn: F) -> ScopeGuard<T, F, OnSuccess>
        where F: FnOnce(T)
    {
        ScopeGuard::with_strategy(v, dropfn)
    }

    /// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.
    ///
    /// Requires crate feature `use_std`.
    ///
    /// ## Examples
    ///
    /// For performance reasons, or to emulate “only run guard on unwind” in
    /// no-std environments, we can also use the default guard and simply manually
    /// defuse it at the end of scope like the following example. (The performance
    /// reason would be if the [`OnUnwind`]'s call to [std::thread::panicking()] is
    /// an issue.)
    ///
    /// ```
    /// extern crate scopeguard;
    ///
    /// use scopeguard::ScopeGuard;
    /// # fn main() {
    /// {
    ///     let guard = scopeguard::guard((), |_| {});
    ///
    ///     // rest of the code here
    ///
    ///     // we reached the end of scope without unwinding - defuse it
    ///     ScopeGuard::into_inner(guard);
    /// }
    /// # }
    /// ```
    #[cfg(feature = "use_std")]
    #[inline]
    pub fn guard_on_unwind<T, F>(v: T, dropfn: F) -> ScopeGuard<T, F, OnUnwind>
        where F: FnOnce(T)
    {
        ScopeGuard::with_strategy(v, dropfn)
    }

    // ScopeGuard can be Sync even if F isn't because the closure is
    // not accessible from references.
    // The guard does not store any instance of S, so it is also irrelevant.
    unsafe impl<T, F, S> Sync for ScopeGuard<T, F, S>
        where T: Sync,
              F: FnOnce(T),
              S: Strategy
    {}

    impl<T, F, S> Deref for ScopeGuard<T, F, S>
        where F: FnOnce(T),
              S: Strategy
    {
        type Target = T;

        fn deref(&self) -> &T {
            &*self.value
        }
    }

    impl<T, F, S> DerefMut for ScopeGuard<T, F, S>
        where F: FnOnce(T),
              S: Strategy
    {
        fn deref_mut(&mut self) -> &mut T {
            &mut *self.value
        }
    }

    impl<T, F, S> Drop for ScopeGuard<T, F, S>
        where F: FnOnce(T),
              S: Strategy
    {
        fn drop(&mut self) {
            // This is OK because the fields are `ManuallyDrop`s
            // which will not be dropped by the compiler.
            let (value, dropfn) = unsafe {
                (ptr::read(&*self.value), ptr::read(&*self.dropfn))
            };
            if S::should_run() {
                dropfn(value);
            }
        }
    }

    impl<T, F, S> fmt::Debug for ScopeGuard<T, F, S>
        where T: fmt::Debug,
              F: FnOnce(T),
              S: Strategy
    {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_struct(stringify!(ScopeGuard))
             .field("value", &*self.value)
             .finish()
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use std::cell::Cell;
        use std::panic::catch_unwind;
        use std::panic::AssertUnwindSafe;

        #[test]
        fn test_defer() {
            let drops = Cell::new(0);
            defer!(drops.set(1000));
            assert_eq!(drops.get(), 0);
        }

        #[cfg(feature = "use_std")]
        #[test]
        fn test_defer_success_1() {
            let drops = Cell::new(0);
            {
                defer_on_success!(drops.set(1));
                assert_eq!(drops.get(), 0);
            }
            assert_eq!(drops.get(), 1);
        }

        #[cfg(feature = "use_std")]
        #[test]
        fn test_defer_success_2() {
            let drops = Cell::new(0);
            let _ = catch_unwind(AssertUnwindSafe(|| {
                defer_on_success!(drops.set(1));
                panic!("failure")
            }));
            assert_eq!(drops.get(), 0);
        }

        #[cfg(feature = "use_std")]
        #[test]
        fn test_defer_unwind_1() {
            let drops = Cell::new(0);
            let _ = catch_unwind(AssertUnwindSafe(|| {
                defer_on_unwind!(drops.set(1));
                assert_eq!(drops.get(), 0);
                panic!("failure")
            }));
            assert_eq!(drops.get(), 1);
        }

        #[cfg(feature = "use_std")]
        #[test]
        fn test_defer_unwind_2() {
            let drops = Cell::new(0);
            {
                defer_on_unwind!(drops.set(1));
            }
            assert_eq!(drops.get(), 0);
        }

        #[test]
        fn test_only_dropped_by_closure_when_run() {
            let value_drops = Cell::new(0);
            let value = guard((), |()| value_drops.set(1 + value_drops.get()));
            let closure_drops = Cell::new(0);
            let guard = guard(value, |_| closure_drops.set(1 + closure_drops.get()));
            assert_eq!(value_drops.get(), 0);
            assert_eq!(closure_drops.get(), 0);
            drop(guard);
            assert_eq!(value_drops.get(), 1);
            assert_eq!(closure_drops.get(), 1);
        }

        #[cfg(feature = "use_std")]
        #[test]
        fn test_dropped_once_when_not_run() {
            let value_drops = Cell::new(0);
            let value = guard((), |()| value_drops.set(1 + value_drops.get()));
            let captured_drops = Cell::new(0);
            let captured = guard((), |()| captured_drops.set(1 + captured_drops.get()));
            let closure_drops = Cell::new(0);
            let guard = guard_on_unwind(value, |value| {
                drop(value);
                drop(captured);
                closure_drops.set(1 + closure_drops.get())
            });
            assert_eq!(value_drops.get(), 0);
            assert_eq!(captured_drops.get(), 0);
            assert_eq!(closure_drops.get(), 0);
            drop(guard);
            assert_eq!(value_drops.get(), 1);
            assert_eq!(captured_drops.get(), 1);
            assert_eq!(closure_drops.get(), 0);
        }

        #[test]
        fn test_into_inner() {
            let dropped = Cell::new(false);
            let value = guard(42, |_| dropped.set(true));
            let guard = guard(value, |_| dropped.set(true));
            let inner = ScopeGuard::into_inner(guard);
            assert_eq!(dropped.get(), false);
            assert_eq!(*inner, 42);
        }
    }