std::mem::ManuallyDrop - Rust
Description: API documentation for the Rust `ManuallyDrop` union in crate `std`.
Keywords: rust, rustlang, rust-lang, ManuallyDrop

# Union std::mem::ManuallyDrop 1.20.0 [−] [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>`
[src]

#### `fn new(value: T) -> ManuallyDrop<T>`

Wrap a value to be manually dropped.

# Examples

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

#### `fn into_inner(slot: ManuallyDrop<T>) -> T`

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

#### `unsafe fn drop(slot: &mut ManuallyDrop<T>)`

Manually drops the contained value.

# Unsafety

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> Deref for ManuallyDrop<T>`
[src]

#### `type Target = T`

The resulting type after dereferencing

#### `fn deref(&self) -> &<ManuallyDrop<T> as Deref>::Target`

The method called to dereference a value

### `impl<T> DerefMut for ManuallyDrop<T>`
[src]

#### `fn deref_mut(&mut self) -> &mut <ManuallyDrop<T> as Deref>::Target`

The method called to mutably dereference a value

### `impl<T> Debug for ManuallyDrop<T> where
T: Debug,`
[src]

#### `fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error>`

Formats the value using the given formatter.

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