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| 1 | +use crate::fmt::{self, Debug}; |
| 2 | +use crate::mem::ManuallyDrop; |
| 3 | +use crate::ops::{Deref, DerefMut}; |
| 4 | + |
| 5 | +/// Wrap a value and run a closure when dropped. |
| 6 | +/// |
| 7 | +/// This is useful for quickly creating desructors inline. |
| 8 | +/// |
| 9 | +/// # Examples |
| 10 | +/// |
| 11 | +/// ```rust |
| 12 | +/// # #![allow(unused)] |
| 13 | +/// #![feature(drop_guard)] |
| 14 | +/// |
| 15 | +/// use std::mem::DropGuard; |
| 16 | +/// |
| 17 | +/// { |
| 18 | +/// // Create a new guard around a string that will |
| 19 | +/// // print its value when dropped. |
| 20 | +/// let s = String::from("Chashu likes tuna"); |
| 21 | +/// let mut s = DropGuard::new(s, |s| println!("{s}")); |
| 22 | +/// |
| 23 | +/// // Modify the string contained in the guard. |
| 24 | +/// s.push_str("!!!"); |
| 25 | +/// |
| 26 | +/// // The guard will be dropped here, printing: |
| 27 | +/// // "Chashu likes tuna!!!" |
| 28 | +/// } |
| 29 | +/// ``` |
| 30 | +#[unstable(feature = "drop_guard", issue = "144426")] |
| 31 | +#[doc(alias = "ScopeGuard")] |
| 32 | +#[doc(alias = "defer")] |
| 33 | +pub struct DropGuard<T, F> |
| 34 | +where |
| 35 | + F: FnOnce(T), |
| 36 | +{ |
| 37 | + inner: ManuallyDrop<T>, |
| 38 | + f: ManuallyDrop<F>, |
| 39 | +} |
| 40 | + |
| 41 | +impl<T, F> DropGuard<T, F> |
| 42 | +where |
| 43 | + F: FnOnce(T), |
| 44 | +{ |
| 45 | + /// Create a new instance of `DropGuard`. |
| 46 | + /// |
| 47 | + /// # Example |
| 48 | + /// |
| 49 | + /// ```rust |
| 50 | + /// # #![allow(unused)] |
| 51 | + /// #![feature(drop_guard)] |
| 52 | + /// |
| 53 | + /// use std::mem::DropGuard; |
| 54 | + /// |
| 55 | + /// let value = String::from("Chashu likes tuna"); |
| 56 | + /// let guard = DropGuard::new(value, |s| println!("{s}")); |
| 57 | + /// ``` |
| 58 | + #[unstable(feature = "drop_guard", issue = "144426")] |
| 59 | + #[must_use] |
| 60 | + pub const fn new(inner: T, f: F) -> Self { |
| 61 | + Self { inner: ManuallyDrop::new(inner), f: ManuallyDrop::new(f) } |
| 62 | + } |
| 63 | + |
| 64 | + /// Consumes the `DropGuard`, returning the wrapped value. |
| 65 | + /// |
| 66 | + /// This will not execute the closure. This is implemented as an associated |
| 67 | + /// function to prevent any potential conflicts with any other methods called |
| 68 | + /// `into_inner` from the `Deref` and `DerefMut` impls. |
| 69 | + /// |
| 70 | + /// It is typically preferred to call this function instead of `mem::forget` |
| 71 | + /// because it will return the stored value and drop variables captured |
| 72 | + /// by the closure instead of leaking their owned resources. |
| 73 | + /// |
| 74 | + /// # Example |
| 75 | + /// |
| 76 | + /// ```rust |
| 77 | + /// # #![allow(unused)] |
| 78 | + /// #![feature(drop_guard)] |
| 79 | + /// |
| 80 | + /// use std::mem::DropGuard; |
| 81 | + /// |
| 82 | + /// let value = String::from("Nori likes chicken"); |
| 83 | + /// let guard = DropGuard::new(value, |s| println!("{s}")); |
| 84 | + /// assert_eq!(DropGuard::into_inner(guard), "Nori likes chicken"); |
| 85 | + /// ``` |
| 86 | + #[unstable(feature = "drop_guard", issue = "144426")] |
| 87 | + #[inline] |
| 88 | + pub fn into_inner(guard: Self) -> T { |
| 89 | + // First we ensure that dropping the guard will not trigger |
| 90 | + // its destructor |
| 91 | + let mut guard = ManuallyDrop::new(guard); |
| 92 | + |
| 93 | + // Next we manually read the stored value from the guard. |
| 94 | + // |
| 95 | + // SAFETY: this is safe because we've taken ownership of the guard. |
| 96 | + let value = unsafe { ManuallyDrop::take(&mut guard.inner) }; |
| 97 | + |
| 98 | + // Finally we drop the stored closure. We do this *after* having read |
| 99 | + // the value, so that even if the closure's `drop` function panics, |
| 100 | + // unwinding still tries to drop the value. |
| 101 | + // |
| 102 | + // SAFETY: this is safe because we've taken ownership of the guard. |
| 103 | + unsafe { ManuallyDrop::drop(&mut guard.f) }; |
| 104 | + value |
| 105 | + } |
| 106 | +} |
| 107 | + |
| 108 | +#[unstable(feature = "drop_guard", issue = "144426")] |
| 109 | +impl<T, F> Deref for DropGuard<T, F> |
| 110 | +where |
| 111 | + F: FnOnce(T), |
| 112 | +{ |
| 113 | + type Target = T; |
| 114 | + |
| 115 | + fn deref(&self) -> &T { |
| 116 | + &*self.inner |
| 117 | + } |
| 118 | +} |
| 119 | + |
| 120 | +#[unstable(feature = "drop_guard", issue = "144426")] |
| 121 | +impl<T, F> DerefMut for DropGuard<T, F> |
| 122 | +where |
| 123 | + F: FnOnce(T), |
| 124 | +{ |
| 125 | + fn deref_mut(&mut self) -> &mut T { |
| 126 | + &mut *self.inner |
| 127 | + } |
| 128 | +} |
| 129 | + |
| 130 | +#[unstable(feature = "drop_guard", issue = "144426")] |
| 131 | +impl<T, F> Drop for DropGuard<T, F> |
| 132 | +where |
| 133 | + F: FnOnce(T), |
| 134 | +{ |
| 135 | + fn drop(&mut self) { |
| 136 | + // SAFETY: `DropGuard` is in the process of being dropped. |
| 137 | + let inner = unsafe { ManuallyDrop::take(&mut self.inner) }; |
| 138 | + |
| 139 | + // SAFETY: `DropGuard` is in the process of being dropped. |
| 140 | + let f = unsafe { ManuallyDrop::take(&mut self.f) }; |
| 141 | + |
| 142 | + f(inner); |
| 143 | + } |
| 144 | +} |
| 145 | + |
| 146 | +#[unstable(feature = "drop_guard", issue = "144426")] |
| 147 | +impl<T, F> Debug for DropGuard<T, F> |
| 148 | +where |
| 149 | + T: Debug, |
| 150 | + F: FnOnce(T), |
| 151 | +{ |
| 152 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 153 | + fmt::Debug::fmt(&**self, f) |
| 154 | + } |
| 155 | +} |
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