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

[David Sweeris]

> On Feb 23, 2017, at 14:44, David Sweeris <davesweeris at mac.com> wrote:
> 
> 
>>> On Feb 23, 2017, at 2:33 PM, Karl Wagner <razielim at gmail.com> wrote:
>>> 
>>> 
>>> 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.
> 
> (replying to bolded part)
> 
> Not necessarily... Complex numbers can conform to `ExpressibleByIntegerLiteral` but not `Comparable`. At least not in a generally-accepted way.

Perhaps a better example would be the `%` operator, since it involves stdlib types. Floating point types are ExpressibleByIntegerLiteral, but don't have the % operator that integers have.

- Dave Sweeris
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