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

[Xiaodi Wu]

On Tue, Feb 21, 2017 at 4:04 PM, Karl Wagner via swift-evolution <
swift-evolution at swift.org> wrote:

>
> On 21 Feb 2017, at 21:39, Max Moiseev <moiseev at apple.com> wrote:
>
>
> On Feb 18, 2017, at 12:02 PM, Karl Wagner via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> I assume the “SignedNumber” protocol is the same as the existing one in
> the standard library. That is to say, Strideable.Stride will now conform to
> Number and have operators.
>
> SignedNumber will *not* be the same. It is just the same name.
> Stride will have operators, yes. Strideable in general will not, unless
> it’s a _Pointer. (you can find the current implementation prototype here
> <https://github.com/apple/swift/blob/new-integer-protocols/stdlib/public/core/Stride.swift.gyb>
> ).
>
>
> Currently, it’s difficult to work with Strideable because you can
> calculate distances between them (as type Strideable.Stride), but you can’t
> add those distances because Strideable.Stride is only constrained to
> conform to “SignedNumber”, which is a pretty useless protocol.
>
> In the prototype, Strideable.Stride has now been changed, so it is
> constrained to “SignedArithmetic” (which, apparently, is to be renamed
> “SignedNumber”). So essentially, the existing SignedNumber has been
> re-parented to “Number” and gains operations such as addition. That’s great!
>
> I think it would be worth including Strideable in the “big picture” in the
> proposal/manifesto, showing how it fits in..
>
>
> Also minor nitpick, would it be too onerous to require Number.Magnitude to
> be Comparable? Currently it’s only Equatable and
> ExpressibleByIntegerLiteral.
>
> Magnitude is supposed to conform to Arithmetic (or Number, or whatever it
> ends up being called), but the recursive constraints feature is missing,
> therefore we constrained it with the protocols that Arithmetic itself
> refines.
>
> Why would you want Comparable?
>
> Max
>
>
> I suppose that leads me on to the question of why Number itself only
> requires that conformers be (Equatable & ExpressibleByIntegerLiteral) and
> does not require that they be Comparable.
>
> If I must be able to create any “Number" out of thin air with an integer
> literal, is it not reasonable to also require that I am able to compare two
> instances?
>
> Are there Number types which can’t be Comparable?
>

Complex numbers. I believe `Number` is designed to allow a complex number
type to conform.


>
> - Karl
>
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