Function core::mem::transmute_copy

pub unsafe fn transmute_copy<T, U>(src: &T) -> U

Interprets src as &U, and then reads src without moving the contained value.

This function will unsafely assume the pointer src is valid for sizeof(U) bytes by transmuting &T to &U and then reading the &U. It will also unsafely create a copy of the contained value instead of moving out of src.

It is not a compile-time error if T and U have different sizes, but it is highly encouraged to only invoke this function where T and U have the same size. This function triggers undefined behavior if U is larger than T.

Examples

fn main() { use std::mem; #[repr(packed)] struct Foo { bar: u8, } let foo_slice = [10u8]; unsafe { // Copy the data from 'foo_slice' and treat it as a 'Foo' let mut foo_struct: Foo = mem::transmute_copy(&foo_slice); assert_eq!(foo_struct.bar, 10); // Modify the copied data foo_struct.bar = 20; assert_eq!(foo_struct.bar, 20); } // The contents of 'foo_slice' should not have changed assert_eq!(foo_slice, [10]); }

use std::mem;

#[repr(packed)]
struct Foo {
    bar: u8,
}

let foo_slice = [10u8];

unsafe {
    // Copy the data from 'foo_slice' and treat it as a 'Foo'
    let mut foo_struct: Foo = mem::transmute_copy(&foo_slice);
    assert_eq!(foo_struct.bar, 10);

    // Modify the copied data
    foo_struct.bar = 20;
    assert_eq!(foo_struct.bar, 20);
}

// The contents of 'foo_slice' should not have changed
assert_eq!(foo_slice, [10]);