Union core::mem::ManuallyDrop1.20.0 [] [src]

pub union ManuallyDrop<T> {
    // some 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>
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Wrap a value to be manually dropped.

Examples

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

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Extract the value from the ManuallyDrop container.

Examples

use std::mem::ManuallyDrop;
let x = ManuallyDrop::new(Box::new(()));
let _: Box<()> = ManuallyDrop::into_inner(x);Run

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Manually drops the contained value.

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: Copy> Copy for ManuallyDrop<T>
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impl<T> Deref for ManuallyDrop<T>
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The resulting type after dereferencing.

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Dereferences the value.

impl<T> DerefMut for ManuallyDrop<T>
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Mutably dereferences the value.

impl<T: Debug> Debug for ManuallyDrop<T>
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Formats the value using the given formatter.

impl<T: Clone> Clone for ManuallyDrop<T>
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Returns a copy of the value. Read more

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Performs copy-assignment from source. Read more

impl<T: Default> Default for ManuallyDrop<T>
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Returns the "default value" for a type. Read more

impl<T: PartialEq> PartialEq for ManuallyDrop<T>
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This method tests for self and other values to be equal, and is used by ==. Read more

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This method tests for !=.

impl<T: Eq> Eq for ManuallyDrop<T>
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impl<T: PartialOrd> PartialOrd for ManuallyDrop<T>
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This method returns an ordering between self and other values if one exists. Read more

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This method tests less than (for self and other) and is used by the < operator. Read more

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This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

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This method tests greater than (for self and other) and is used by the > operator. Read more

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This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

impl<T: Ord> Ord for ManuallyDrop<T>
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This method returns an Ordering between self and other. Read more

1.21.0
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Compares and returns the maximum of two values. Read more

1.21.0
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Compares and returns the minimum of two values. Read more

impl<T: Hash> Hash for ManuallyDrop<T>
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Feeds this value into the given [Hasher]. Read more

1.3.0
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Feeds a slice of this type into the given [Hasher]. Read more