[swift-evolution] [RFC] #Self

[Matthew Johnson]

Sent from my iPad

> On May 10, 2016, at 12:59 PM, Thorsten Seitz <tseitz42 at icloud.com> wrote:
> 
> 
>> Am 10.05.2016 um 18:41 schrieb Timothy Wood via swift-evolution <swift-evolution at swift.org>:
>> 
>> 
>>> On May 10, 2016, at 9:28 AM, Matthew Johnson <matthew at anandabits.com> wrote:
>>> Yep, understood.  It's perfectly clear to me but I understand why Chris is concerned about it having potential to confuse people.  It is a pretty subtle difference especially since Self and #Self are the same in some contexts.  In any case, I would be content to live with any name that wins out.
>> 
>> Ah, OK -- it sounds like we just differ on what would be least confusing =)
>> 
>> The other proposed name of #StaticSelf, seems like it would be very clear (if a bit redundant and longer than needed, once you’ve come across it once or twice). I could certainly live with #StaticSelf.
> 
> In that case StaticSelf would be sufficient IMHO. The # should only be needed to distinguish between Self and #Self.
> 
> So:
> 
> Self, #Self
> Self, StaticSelf
> DynamicSelf, StaticSelf
> 
> 
> As far as I understand #Self should be the type of the implementor (ImplementorSelf?) or conforming type (ConformingSelf?).
> How would this work with default methods?
> 
> protocol A {
>    func f() -> #Self
>    init()
> }
> 
> extension A {
>    func f() -> #Self { return init() }    // what type has #Self here?
> }

The conforming type.  C in your example.  If we have 'class D: C' and it overrides 'f' the override would have a return type of C, not D.  The returned instance could be of type D since it is a subtype of C.  We could also explore allowing overrides to have a covariant return type, it just wouldn't be visible when accessed via the protocol through a generic constraint or an existential (those would only guarantee C, the type that declared the conformance.

> 
> class C : A {}
> 
> let c = C().f()    // what type has c here?
> 
> -Thorsten