The post says

  The new API to cast in an unsafe manner is:

  let x: f32 = 1.0;
  let y: u8 = unsafe { x.to_int_unchecked() };

  But as always, you should only use this method as a last resort. Just like with array access, the compiler can often optimize the checks away, making the safe and unsafe versions equivalent when the compiler can prove it.

I believe for array access you can elide the bounds checking with an assert like

  assert!(len(arr) <= 255)
  let mut sum = 0;
  for i in 0..255 {
    sum += arr[i];//this access doesn't emit bounds checks in the compiled code
  }

I'm guessing it would work like this with casts?

  assert!(x <= 255. && x >= 0);
  let y: u8 = x as u8; // no check