#![feature(slice_from_raw_parts)]
use std::ptr;

// create a slice pointer when starting out with a pointer to the first element
let mut x = [5, 6, 7];
let ptr = &mut x[0] as *mut _;
let slice = ptr::slice_from_raw_parts_mut(ptr, 3);
assert_eq!(unsafe { &*slice }[2], 7);