1.20.0[][src]Struct std::mem::ManuallyDrop

#[lang = "manually_drop"] #[repr(transparent)]
pub struct ManuallyDrop<T> where
    T: ?Sized
{ /* fields omitted */ }

A wrapper to inhibit compiler from automatically calling T’s destructor.

This wrapper is 0-cost.

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>
[src]

Wrap a value to be manually dropped.

Examples

use std::mem::ManuallyDrop;
ManuallyDrop::new(Box::new(()));Run

Extract 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

🔬 This is a nightly-only experimental API. (manually_drop_take #55422)

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
[src]

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.

Trait Implementations

impl<T> Debug for ManuallyDrop<T> where
    T: Debug + ?Sized
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impl<T> DerefMut for ManuallyDrop<T> where
    T: ?Sized
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impl<T> Deref for ManuallyDrop<T> where
    T: ?Sized
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The resulting type after dereferencing.

impl<T> Clone for ManuallyDrop<T> where
    T: Clone + ?Sized
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Performs copy-assignment from source. Read more

impl<T> PartialOrd<ManuallyDrop<T>> for ManuallyDrop<T> where
    T: PartialOrd<T> + ?Sized
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impl<T> Ord for ManuallyDrop<T> where
    T: Ord + ?Sized
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Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

impl<T> Eq for ManuallyDrop<T> where
    T: Eq + ?Sized
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impl<T> PartialEq<ManuallyDrop<T>> for ManuallyDrop<T> where
    T: PartialEq<T> + ?Sized
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impl<T> Hash for ManuallyDrop<T> where
    T: Hash + ?Sized
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Feeds a slice of this type into the given [Hasher]. Read more

impl<T> Default for ManuallyDrop<T> where
    T: Default + ?Sized
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impl<T> Copy for ManuallyDrop<T> where
    T: Copy + ?Sized
[src]

Auto Trait Implementations

impl<T: ?Sized> Send for ManuallyDrop<T> where
    T: Send

impl<T: ?Sized> Sync for ManuallyDrop<T> where
    T: Sync

Blanket Implementations

impl<T, U> TryFrom for T where
    T: From<U>, 
[src]

🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

impl<T> From for T
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impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

impl<T, U> Into for T where
    U: From<T>, 
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impl<T> Borrow for T where
    T: ?Sized
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impl<T> BorrowMut for T where
    T: ?Sized
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impl<T> Any for T where
    T: 'static + ?Sized
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impl<T> ToOwned for T where
    T: Clone
[src]