[swift-evolution] specialize a generic type in a method

[Vladimir.S]

On 21.06.2016 18:59, Charlie Monroe wrote:
> This may change a lot if once existentials proposal gets approved and implemented...
>
>
>> On Jun 21, 2016, at 5:20 PM, Vladimir.S <svabox at gmail.com> wrote:
>>
>> On 20.06.2016 21:38, Charlie Monroe wrote:
>>> Something like this should work:
>>>
>>> protocol P1 {
>>> 	associatedtype T
>>> 	func foo(t: T)
>>> 	func bar<U where U == T, U: Equatable>(t: U)
>>> }
>>>

Seems like your suggestion will not work. Doug Gregor : "This should be 
ill-formed. "bar" isn't actually a generic function. If we want this 
behavior, we should explicitly support it with "where" clauses on 
non-generic declarations." (https://bugs.swift.org/browse/SR-1849)

Checking if there is another solution for this.

>>
>> Thank you. Strange, but also can't check this code - compiler crashes on it.
>>
>> IMO it will be good if we can write just
>>
>> func bar(t: T & Equatable)
>>
>>>
>>>> On Jun 20, 2016, at 8:07 PM, Vladimir.S <svabox at gmail.com> wrote:
>>>>
>>>> Thank you for reply. Yes, seems this could be solved by extension. No other solutions?
>>>>
>>>> But how should I be if I need such a protocol?
>>>>
>>>> protocol P1 {
>>>>   associatedtype T
>>>>   func foo(t: T)
>>>>   func bar(t: T) // where T:Equatable  ??
>>>> }
>>>>
>>>> I.e. I need to specify T & Equatable for bar in requirements
>>>>
>>>> On 20.06.2016 20:03, Charlie Monroe wrote:
>>>>> This is IMHO better solved via an extension - it even makes more sense to put together methods whose use is limited only to certain generics constraint:
>>>>>
>>>>> extension Foo where I: Equatable {
>>>>>
>>>>> 	func bar(i: I) {
>>>>> 		///
>>>>> 	}
>>>>>
>>>>> }
>>>>>
>>>>>
>>>>>> On Jun 20, 2016, at 6:57 PM, Vladimir.S via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>>
>>>>>> Should we be able to specialize a generic type in a method, if that generic type declared in type's definition like here? :
>>>>>>
>>>>>> struct Foo<I> {
>>>>>>  func bar(i: I) where I: Equatable { } // should this work?
>>>>>> }
>>>>>>
>>>>>> As I understand, for concrete instance of foo: Foo<X>, if X is not Equatable, then compiler should prevent us from calling foo.bar(x)
>>>>>>
>>>>>> Or, probably, the better way to express this could be :
>>>>>>
>>>>>>  func bar(i: I & Equatable) { }
>>>>>> or
>>>>>>  func bar(i: Any<I, Equatable>) { }
>>>>>>
>>>>>> Can't check if it possible now because my compiler crashes because of 'where I:Equatable' text (submitted to bugs.swift.org)
>>>>>> _______________________________________________
>>>>>> swift-evolution mailing list
>>>>>> swift-evolution at swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>
>>>>>
>>>
>>>
>
>