[swift-evolution] [Re-Review] SE-0104: Protocol-oriented integers

[Karl Wagner]

> On 23 Feb 2017, at 19:40, Max Moiseev <moiseev at apple.com> wrote:
> 
> Conformance to Comparable is not required by anything in the standard library. Besides, it is always possible to further constrain your own code as in:
> 

Besides FloatingPoint, you mean? Or Collection indexes? Quite a lot of stuff, actually.

> func f<T : Number>(_ x: T) where T.Magnitude : Comparable {}
> 
> I would argue that adding constraints without solid proof of them being useful and necessary is not the right thing to do.
> Also, sorting things by magnitude will require using a predicate-based sorted() anyway, and that does not require Comparable.
> 
> Max

Yes, but the constraints in the standard library should also convey some meaning and be useful. What do we mean by a “magnitude” anyway? Won’t it be strange in practice that I can create a “magnitude” out of nothing but an arbitrary integer literal but can’t compare two values? Ultimately it looks like a deficiency in the design to me - either it’s a simple scalar, ExpressibleByIntegerLiteral and Comparable, or it’s something more complex and can’t be either.

This is exactly the kind of flaw I’ve been working around with the current Strideable.Stride (i.e. current SignedNumber). If a type is ExpressibleByIntegerLiteral, you should be able to basically do all the things to it that you can do with an integer.

- Karl