How to convert Weight to u64 and the other way around

Question

If I wanted to do some basic arithmetic operations on some weight it would be possible to do so using saturating_* methods.

But what if I wanted to multiply it with a fraction(e.g. Perbill)? How could I convert the weight into u64 so that I can do the above mentioned operation, and how could I convert it back to the Weight type?

Answer 1

How to convert Weight to u64 and the other way around

You cannot convert Weigth to a single u64, since it is (currently) two dimensional. You can split and construct it from its components like this:

let weight = Weight::from_parts(10, 20);
let ref_time = weight.ref_time();
let proof_size = weight.proof_size();
let weight = Weight::from_parts(ref_time, proof_size);

But what if I wanted to multiply it with a fraction(e.g. Perbill)?

Well... just do it?

#[test]
fn per_thing_mul_works() {
    let weight = Weight::from_parts(80, 60);
    let half = sp_arithmetic::Perbill::from_percent(50);

    assert_eq!(weight * half, Weight::from_parts(40, 30));
    assert_eq!(half * weight, Weight::from_parts(40, 30));
}