[swift-evolution] [Manifesto] Completing Generics

[T.J. Usiyan]

> Since Swift doesn't allow overloading on return type
>


Swift definitely allows overloading on return type.



>
> On 10 March 2016 at 13:07, Joe Groff <jgroff at apple.com> wrote:
>
>>
>> > On Mar 9, 2016, at 6:02 PM, Howard Lovatt <howard.lovatt at gmail.com>
>> wrote:
>> >
>> > Wow, I would never have guessed that syntax :)
>> >
>> > It makes no sense to me to interpret a generic constraint as meaning
>> all instead of any. How could anything either accept or return all possible
>> implementations of something simultaneously, surely it only ever accepts or
>> returns one of all the possible implementations at a time.
>>
>> A type variable in angle brackets always means "all". It's like a
>> function parameter, but at type level—it's in the caller's hands what it
>> gets bound to. You couldn't write a function `func foo<Input,
>> Output>(Input) -> Output` unless that function was able to generate a value
>> of every possible type a caller might pass in for Output, just like you
>> couldn't write e.g. 'absolute value' as taking its result as a second
>> parameter.
>>
>> >
>> > If the interpretation for output is that at time 1 it returns one of
>> all the possible implementations at at time 2  returns another - then that
>> is what I want. However I would describe that as returning one of the
>> possible implementations, not all.
>> >
>> > But no doubt you are correct, since you probably wrote that bit of the
>> compiler :(
>> >
>> > More practical points
>> >
>> >  1. My compiler, 7.3 beta (7D152p), rejects the syntax, it doesn't like
>> where inside Any<> saying it expects > to complete generic argument list.
>> When will this be available, so that I can try it out?
>> >  2. Will the declarations inside protocols also change to the Any<...>
>> form or will all the generics remain following the function name rather in
>> a returned Any<...>? Currently -> Any<...> doesn't work in protocols for me.
>> >  3. In the construct Any<Protocol where Type == Type>, i.e. same type
>> name used in protocol and enclosing struct/class/extension, does the left
>> Type refer to the protocol or the enclosing struct/class/extension?
>> >  4. Is there any documentation of all of this?
>>
>> Sorry, this is all possible future syntax and features. It's not
>> implemented today. You'd need to write your own equivalent of the "Any"
>> wrapper by hand right now.
>>
>> -Joe
>>
>>
>
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