#![allow(unused_variables)]
#![feature(get_mut_unchecked)]
#![feature(allocator_api)]
fn main() {
    use std::sync::Arc;
    use std::alloc::System;
    let mut five = Arc::<u32, _>::new_uninit_in(System);
    let five = unsafe {
        Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5);
        five.assume_init()
    };
    assert_eq!(* five, 5)
}