#![allow(unused_variables)]
#![feature(allocator_api, box_vec_non_null)]
use std::alloc::{AllocError, Allocator, Global, Layout};
fn main() {
    let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
    let vec = unsafe {
        let mem = match Global.allocate(layout) {
            Ok(mem) => mem.cast::<u32>(),
            Err(AllocError) => return,
        };
        mem.write(1_000_000);
        Vec::from_parts_in(mem, 1, 16, Global)
    };
    assert_eq!(vec, & [1_000_000]);
    assert_eq!(vec.capacity(), 16);
}