Pre-RFC: Add explicitly-named numeric conversion APIs

libs
19

I did some experimenting in this area and wrote the az crate, which uses traits.

  • You can write i.az::<O>() or cast::<I, O>(i) instead of i as O, with overflow panicking with debug_assertions or wrapping otherwise.
  • There are other traits/casts for checked, saturating, wrapping and overflowing conversions, e.g. i.checked_as::<O>().
  • For floating-point to integer conversions I chose truncation by default, but rounding is supported via a Round wrapper, so that
    assert_eq!(0.6f32.az::<i32>(), 0);
assert_eq!(Round(0.6f32).az::<i32>(), 1);
// Ties round to even.
assert_eq!(Round(0.5f32).az::<i32>(), 0);
assert_eq!(Round(1.5f32).az::<i32>(), 2);
  • I also wrote conversions into e.g Wrapping<i32>, which does wrapping.
  • For floating-point to integer conversions I used bitwise manipulation instead of intrinsic conversions as it wasn't clear what the guarantees where; this is probably much slower but every behavior is defined. And I was more interested in the API at this point.
2 Likes