use std::boxed::Box;
use std::mem;

unsafe fn alloc<T>(count: usize) -> Box<[T]> {
    let mut allocated = Vec::with_capacity(count);
    allocated.set_len(count); // If you don't do this, the vec will be trimmed.
    allocated.into_boxed_slice()
}

fn main() {
    println!("{}", unsafe {
        const REGION_SIZE: usize = 4;
        let mut region: Box<[u8]> = alloc(REGION_SIZE);
        *(region.as_mut_ptr() as *mut u32) = 0x73746974;
        let string = String::from_raw_parts(
            region.as_mut_ptr(),
            REGION_SIZE,
            REGION_SIZE,
        );
        mem::forget(region); // `String::from_raw_parts` took ownership
        string
    });
}