#![allow(unused_variables)]
#![feature(allocator_api)]
fn main() {
    use std::alloc::System;
    let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System);
    values[0].write(1);
    values[1].write(2);
    values[2].write(3);
    let values = unsafe { values.assume_init() };
    assert_eq!(* values, [1, 2, 3])
}