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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`.
    }
}

Methods

impl<T> ManuallyDrop<T> [src]

Wrap a value to be manually dropped.

Examples

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

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`.

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> Hash for ManuallyDrop<T> where
    T: Hash + ?Sized
[src]

Feeds this value into the given [Hasher]. Read more

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

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

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

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

This method returns an ordering between self and other values if one exists. Read more

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

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

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

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

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

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

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

Formats the value using the given formatter. Read more

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

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

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

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

impl<T> DerefMut for ManuallyDrop<T> where
    T: ?Sized
[src]

Mutably dereferences the value.

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

Returns the "default value" for a type. Read more

impl<T> Deref for ManuallyDrop<T> where
    T: ?Sized
[src]

The resulting type after dereferencing.

Dereferences the value.

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.

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

Performs the conversion.

impl<T> From for T [src]

Performs the conversion.

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

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

The type returned in the event of a conversion error.

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

Performs the conversion.

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

Performs the conversion.

impl<T> Borrow for T where
    T: ?Sized
[src]

ⓘImportant traits for &'a mut I
impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized, 
    type Item = <I as Iterator>::Item;
impl<'a, R: Read + ?Sized> Read for &'a mut R
impl<'a, W: Write + ?Sized> Write for &'a mut W

Immutably borrows from an owned value. Read more

impl<T> BorrowMut for T where
    T: ?Sized
[src]

ⓘImportant traits for &'a mut I
impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized, 
    type Item = <I as Iterator>::Item;
impl<'a, R: Read + ?Sized> Read for &'a mut R
impl<'a, W: Write + ?Sized> Write for &'a mut W

Mutably borrows from an owned value. Read more

impl<T> Any for T where
    T: 'static + ?Sized
[src]

🔬 This is a nightly-only experimental API. (get_type_id #27745)this method will likely be replaced by an associated static

Gets the TypeId of self. Read more

impl<T> ToOwned for T where
    T: Clone
[src]

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into #41263)recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/mem/struct.ManuallyDrop.html