[swift-evolution] ExpressibleByZeroLiteral

[Xiaodi Wu]

On Fri, Mar 31, 2017 at 11:31 AM, Sasha Lopoukhine <sasha.swi.evo at gmail.com>
wrote:

> Completely forgot about those. Thank you. The point still stands, it
> doesn't really make sense to multiply strides by each other. I don't know
> how this would work, but if we're already ok to shake up the Integer
> protocols, then maybe adding one between SignedNumeric and SignedInteger
> might be ok.
>

The time for shaking up integer protocols is over, though. During that
time, it was considered whether separating Numeric into fields and rings
would be useful, which is what you're asking, but it was thought too
esoteric and rejected in favor of the approved design.


 On 31 Mar 2017, at 17:25, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:

>
> Have you seen the revised integer protocols?
> https://github.com/apple/swift-evolution/blob/master/proposa
> ls/0104-improved-integers.md
>
> `SignedNumeric` will no longer refine `Comparable`. It will, however,
> still require that you can define multiplication.
>
>
> On Fri, Mar 31, 2017 at 11:09 AM, Sasha Lopoukhine via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> Hello everyone!
>>
>> I'd like to discuss the constraint on Strideable. I see no reason to
>> restrict Strideable types to non-circular types. It would be pretty
>> neat/useful to be able to define a type such as a Week, with strides
>> looping around to the start of the enum. Currently, the only reason this is
>> impossible is because of the restriction on Stride that it must conform to
>> SignedNumber.
>>
>> I think that it might be worth looking into defining a new protocol
>> specifically for the constraint on Strideable.Stride, something that looks
>> like this:
>>
>> /// Instances of conforming types can be subtracted, arithmetically
>> /// negated, and initialized from `0`.
>> ///
>> /// Axioms:
>> ///
>> /// - `x - 0 == x`
>> /// - `-x == 0 - x`
>> /// - `-(-x) == x`
>> public protocol StrideProtocol : ExpressibleByIntegerLiteral {
>>
>>     /// Returns the result of negating `x`.
>>     prefix public static func -(x: Self) -> Self
>>
>>     /// Returns the difference between `lhs` and `rhs`.
>>     public static func -(lhs: Self, rhs: Self) -> Self
>> }
>>
>> public typealias SignedNumber = StrideProtocol & Comparable
>>
>> Strideable.Stride could then conform to StrideProtocol, allowing groups
>> etc.
>>
>> WDYT?
>>
>> -- Sasha
>>
>>
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>>
>>
>
>
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