slice-of-zero-size-elements.rs

//@ run-pass
#![allow(stable_features)]

//@ compile-flags: -C debug-assertions

#![feature(iter_to_slice)]

use std::slice;

fn foo<T>(v: &[T]) -> Option<&[T]> {
    let mut it = v.iter();
    for _ in 0..5 {
        let _ = it.next();
    }
    Some(it.as_slice())
}

fn foo_mut<T>(v: &mut [T]) -> Option<&mut [T]> {
    let mut it = v.iter_mut();
    for _ in 0..5 {
        let _ = it.next();
    }
    Some(it.into_slice())
}

pub fn main() {
    // In a slice of zero-size elements the pointer is meaningless.
    // Ensure iteration still works even if the pointer is at the end of the address space.
    let slice: &[()] = unsafe { slice::from_raw_parts(-5isize as *const (), 10) };
    assert_eq!(slice.len(), 10);
    assert_eq!(slice.iter().count(), 10);

    // .nth() on the iterator should also behave correctly
    let mut it = slice.iter();
    assert!(it.nth(5).is_some());
    assert_eq!(it.count(), 4);

    // Converting Iter to a slice should never have a null pointer
    assert!(foo(slice).is_some());

    // Test mutable iterators as well
    let slice: &mut [()] = unsafe { slice::from_raw_parts_mut(-5isize as *mut (), 10) };
    assert_eq!(slice.len(), 10);
    assert_eq!(slice.iter_mut().count(), 10);

    {
        let mut it = slice.iter_mut();
        assert!(it.nth(5).is_some());
        assert_eq!(it.count(), 4);
    }

    assert!(foo_mut(slice).is_some())
}