# Function std::ptr::replace

1.0.0 (const: unstable) · source ·

    pub unsafe fn replace<T>(dst: *mut T, src: T) -> T

Expand description

Moves `src` into the pointed `dst`, returning the previous `dst` value.

Neither value is dropped.

This function is semantically equivalent to `mem::replace` except that it operates on raw pointers instead of references. When references are available, `mem::replace` should be preferred.

## Safety

Behavior is undefined if any of the following conditions are violated:

- `dst` must be valid for both reads and writes.

- `dst` must be properly aligned.

- `dst` must point to a properly initialized value of type `T`.

Note that even if `T` has size `0`, the pointer must be non-null and properly aligned.

## Examples

    use std::ptr;

    let mut rust = vec!['b', 'u', 's', 't'];

    // `mem::replace` would have the same effect without requiring the unsafe
    // block.
    let b = unsafe {
        ptr::replace(&mut rust[0], 'r')
    };

    assert_eq!(b, 'b');
    assert_eq!(rust, &['r', 'u', 's', 't']);

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