rust/tests/run-pass/box.rs

#![feature(ptr_internals)]

fn main() {
    into_raw();
    into_unique();
    boxed_pair_to_vec();
}

fn into_raw() { unsafe {
    let b = Box::new(4i32);
    let r = Box::into_raw(b);

    // "lose the tag"
    let r2 = ((r as usize)+0) as *mut i32;
    *(&mut *r2) = 7;

    // Use original ptr again
    *(&mut *r) = 17;
    drop(Box::from_raw(r));
}}

fn into_unique() { unsafe {
    let b = Box::new(4i32);
    let u = Box::into_unique(b).0;

    // "lose the tag"
    let r = ((u.as_ptr() as usize)+0) as *mut i32;
    *(&mut *r) = 7;

    // Use original ptr again.
    drop(Box::from_raw(u.as_ptr()));
}}

fn boxed_pair_to_vec() {
    #[repr(C)]
    #[derive(Debug)]
    struct PairFoo {
        fst: Foo,
        snd: Foo,
    }

    #[derive(Debug)]
    struct Foo(u64);
    fn reinterstruct(box_pair: Box<PairFoo>) -> Vec<Foo> {
        let ref_pair = Box::leak(box_pair) as *mut PairFoo;
        let ptr_foo = unsafe { &mut (*ref_pair).fst as *mut Foo };
        unsafe {
            Vec::from_raw_parts(ptr_foo, 2, 2)
        }
    }

    let pair_foo = Box::new(PairFoo {
        fst: Foo(42),
        snd: Foo(1337),
    });
    println!("pair_foo = {:?}", pair_foo);
    for (n, foo) in reinterstruct(pair_foo).into_iter().enumerate() {
        println!("foo #{} = {:?}", n, foo);
    }
}