enum-univariant-repr.rs

// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.


use std::mem;

// Univariant C-like enum
#[repr(i32)]
enum Univariant {
    X = 17
}

#[repr(u16)]
enum UnivariantWithoutDescr {
    Y
}

pub fn main() {
    {
        assert_eq!(4, mem::size_of::<Univariant>());
        assert_eq!(17, Univariant::X as i32);

        let enums: &[Univariant] =
            &[Univariant::X, Univariant::X, Univariant::X];
        let ints: &[i32] = unsafe { mem::transmute(enums) };
        // check it has the same memory layout as i32
        assert_eq!(&[17, 17, 17], ints);
    }

    {
        assert_eq!(2, mem::size_of::<UnivariantWithoutDescr>());
        let descr = UnivariantWithoutDescr::Y as u16;

        let enums: &[UnivariantWithoutDescr] =
            &[UnivariantWithoutDescr::Y, UnivariantWithoutDescr::Y, UnivariantWithoutDescr::Y];
        let ints: &[u16] = unsafe { mem::transmute(enums) };
        // check it has the same memory layout as u16
        assert_eq!(&[descr, descr, descr], ints);
    }
}