[swift-evolution] [RFC] #Self

[Matthew Johnson]

Sent from my iPad

> On May 11, 2016, at 7:33 AM, Thorsten Seitz <tseitz42 at icloud.com> wrote:
> 
> 
> 
>> Am 10. Mai 2016 um 20:11 schrieb Matthew Johnson <matthew at anandabits.com>:
>> 
>> 
>> 
>> 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.
> 
> 
> Thanks, that makes sense.
> So within a default method like in extension A above the (concrete) type of #Self is still unknown and I only know that it will conform to A. That's fine. As soon as a non protocol type like a class conforms to the protocol #Self gets fixed to that type and because we have no multiple inheritance for non protocols there is no possibility to create conflicts.

Yep, it's a pretty subtle distinction from Self but will be useful to have.  

> 
> -Thorsten