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

# Function std::mem::transmute_copy 1.0.0 [−] [src]

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

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

This function will unsafely assume the pointer `src` is valid for `size_of::<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

    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]);Run

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