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

Xiaodi Wu xiaodi.wu at gmail.com
Fri Feb 24 18:45:12 CST 2017

That was a deliberate design choice discussed during review of floating
point protocols. Floating point remainder and integer modulo are very
different. Spelling them the same way enables use in generic protocols,
which would be incorrect uses. This was borne out by observation of
erroneous uses of floating point % in Swift 2.
On Fri, Feb 24, 2017 at 18:13 David Sweeris via swift-evolution <
swift-evolution at swift.org> wrote:

> 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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