I would like to see number types have more interfa...

# language-proposals

[benleggiero]

I would like to see number types have more interfaces that they conform to, to let me reason about them better.

For instance, right now I have to have to make separate, specialized versions of classes for each individual number type, like Int64Size vs `Int8Size`:
https://github.com/BlueHuskyStudios/Blue-Base/commit/5baf26fb495b29bd9ad4a7b1099d76c9f0c1c163
Just about all the code between these classes is identical, but solely because I can only say either “Use a `Long`” or “Use any implementation of `Number`“, I have to slowly go through every native number type and make separate implementations for these.

If I could just specify “This is a Size implementation based on a native integer”, I could write it once and let generics fill in the blanks.

Swift did this with a set of 9 interfaces, and it makes it super easy to let the compiler reason about what I’m getting at:
https://developer.apple.com/documentation/swift/swift_standard_library/numbers_and_basic_values/numeric_protocols
https://github.com/apple/swift-evolution/blob/master/proposals/0104-improved-integers.md

[karelpeeters]

Are users allowed to define their own numeric types? If so, how does mixing work in generic code?

[benleggiero]

Yup! Common examples are big integers, 80- and 128-bit binary numbers, etc.

What do you mean by mixing? I can give concrete examples if needed

[karelpeeters]

If I have a function that takes two parameters of type eg. FixedSizeInteger, can I add them together?

[benleggiero]

Since FixedWidthInteger is a protocol (interface) in Swift, it has to be used as a generic constraint instead of a raw parameter type. Additionally, its multiplication function requirements, multipliedFullWidth(by:), multipliedReportingOverflow(by:), and unsafeMultiplied(by:) all require the right-hand side and return to be of the same type as the receiver. So, in Swift:

func exampleMultiply<T: FixedWidthInteger>(lhs: T, rhs: T) -> T {
    return lhs.unsafeMultiply(by: rhs)
}

Perhaps in Kotlin it might look like this:

fun <T: FixedWidthInteger> exampleMultiply(lhs: T, rhs: T) = lhs.unsafeMultiply(by = rhs)

[karelpeeters]

That makes a lot of sense, thanks for explaining. It'd be cool to see this in Kotlin as well.