1.20.0[−][src]Struct std::mem::ManuallyDrop
A wrapper to inhibit compiler from automatically calling T
’s destructor.
This wrapper is 0-cost.
ManuallyDrop<T>
is subject to the same layout optimizations as T
.
As a consequence, it has no effect on the assumptions that the compiler makes
about all values being initialized at their type. In particular, initializing
a ManuallyDrop<&mut T>
with mem::zeroed
is undefined behavior.
If you need to handle uninitialized data, use MaybeUninit<T>
instead.
Examples
This wrapper helps with explicitly documenting the drop order dependencies between fields of the type:
use std::mem::ManuallyDrop; struct Peach; struct Banana; struct Melon; struct FruitBox { // Immediately clear there’s something non-trivial going on with these fields. peach: ManuallyDrop<Peach>, melon: Melon, // Field that’s independent of the other two. banana: ManuallyDrop<Banana>, } impl Drop for FruitBox { fn drop(&mut self) { unsafe { // Explicit ordering in which field destructors are run specified in the intuitive // location – the destructor of the structure containing the fields. // Moreover, one can now reorder fields within the struct however much they want. ManuallyDrop::drop(&mut self.peach); ManuallyDrop::drop(&mut self.banana); } // After destructor for `FruitBox` runs (this function), the destructor for Melon gets // invoked in the usual manner, as it is not wrapped in `ManuallyDrop`. } }Run
Methods
impl<T> ManuallyDrop<T>
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pub const fn new(value: T) -> ManuallyDrop<T>
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Wrap a value to be manually dropped.
Examples
use std::mem::ManuallyDrop; ManuallyDrop::new(Box::new(()));Run
pub const fn into_inner(slot: ManuallyDrop<T>) -> T
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Extracts the value from the ManuallyDrop
container.
This allows the value to be dropped again.
Examples
use std::mem::ManuallyDrop; let x = ManuallyDrop::new(Box::new(())); let _: Box<()> = ManuallyDrop::into_inner(x); // This drops the `Box`.Run
#[must_use = "if you don\'t need the value, you can use `ManuallyDrop::drop` instead"]
pub unsafe fn take(slot: &mut ManuallyDrop<T>) -> T
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Takes the contained value out.
This method is primarily intended for moving out values in drop.
Instead of using ManuallyDrop::drop
to manually drop the value,
you can use this method to take the value and use it however desired.
Drop
will be invoked on the returned value following normal end-of-scope rules.
If you have ownership of the container, you can use ManuallyDrop::into_inner
instead.
Safety
This function semantically moves out the contained value without preventing further usage. It is up to the user of this method to ensure that this container is not used again.
impl<T> ManuallyDrop<T> where
T: ?Sized,
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T: ?Sized,
pub unsafe fn drop(slot: &mut ManuallyDrop<T>)
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Manually drops the contained value.
If you have ownership of the value, you can use ManuallyDrop::into_inner
instead.
Safety
This function runs the destructor of the contained value and thus the wrapped value
now represents uninitialized data. It is up to the user of this method to ensure the
uninitialized data is not actually used.
In particular, this function can only be called called at most once
for a given instance of ManuallyDrop<T>
.
Trait Implementations
impl<T> Debug for ManuallyDrop<T> where
T: Debug + ?Sized,
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T: Debug + ?Sized,
impl<T> DerefMut for ManuallyDrop<T> where
T: ?Sized,
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T: ?Sized,
impl<T> Hash for ManuallyDrop<T> where
T: Hash + ?Sized,
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T: Hash + ?Sized,
fn hash<__H>(&self, state: &mut __H) where
__H: Hasher,
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__H: Hasher,
fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0[src]
H: Hasher,
impl<T> Eq for ManuallyDrop<T> where
T: Eq + ?Sized,
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T: Eq + ?Sized,
impl<T> Deref for ManuallyDrop<T> where
T: ?Sized,
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T: ?Sized,
type Target = T
The resulting type after dereferencing.
ⓘImportant traits for &'_ mut Ffn deref(&self) -> &T
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impl<T> Clone for ManuallyDrop<T> where
T: Clone + ?Sized,
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T: Clone + ?Sized,
fn clone(&self) -> ManuallyDrop<T>
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fn clone_from(&mut self, source: &Self)
1.0.0[src]
impl<T> PartialEq<ManuallyDrop<T>> for ManuallyDrop<T> where
T: PartialEq<T> + ?Sized,
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T: PartialEq<T> + ?Sized,
fn eq(&self, other: &ManuallyDrop<T>) -> bool
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fn ne(&self, other: &ManuallyDrop<T>) -> bool
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impl<T> PartialOrd<ManuallyDrop<T>> for ManuallyDrop<T> where
T: PartialOrd<T> + ?Sized,
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T: PartialOrd<T> + ?Sized,
fn partial_cmp(&self, other: &ManuallyDrop<T>) -> Option<Ordering>
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fn lt(&self, other: &ManuallyDrop<T>) -> bool
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fn le(&self, other: &ManuallyDrop<T>) -> bool
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fn gt(&self, other: &ManuallyDrop<T>) -> bool
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fn ge(&self, other: &ManuallyDrop<T>) -> bool
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impl<T> Default for ManuallyDrop<T> where
T: Default + ?Sized,
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T: Default + ?Sized,
fn default() -> ManuallyDrop<T>
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impl<T> Ord for ManuallyDrop<T> where
T: Ord + ?Sized,
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T: Ord + ?Sized,
fn cmp(&self, other: &ManuallyDrop<T>) -> Ordering
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fn max(self, other: Self) -> Self
1.21.0[src]
fn min(self, other: Self) -> Self
1.21.0[src]
fn clamp(self, min: Self, max: Self) -> Self
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impl<T> Copy for ManuallyDrop<T> where
T: Copy + ?Sized,
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T: Copy + ?Sized,
Auto Trait Implementations
impl<T: ?Sized> UnwindSafe for ManuallyDrop<T> where
T: UnwindSafe,
T: UnwindSafe,
impl<T: ?Sized> RefUnwindSafe for ManuallyDrop<T> where
T: RefUnwindSafe,
T: RefUnwindSafe,
impl<T: ?Sized> Unpin for ManuallyDrop<T> where
T: Unpin,
T: Unpin,
impl<T: ?Sized> Send for ManuallyDrop<T> where
T: Send,
T: Send,
impl<T: ?Sized> Sync for ManuallyDrop<T> where
T: Sync,
T: Sync,
Blanket Implementations
impl<T> From<T> for T
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impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
ⓘImportant traits for &'_ mut Ffn borrow_mut(&mut self) -> &mut T
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impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> ToOwned for T where
T: Clone,
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T: Clone,