[swift-users] returning an array of Protocol-conforming objects from a function

[Trent Nadeau]

I think arrays along with other generics are invariant.

On Mon, Jan 25, 2016 at 10:50 PM, Trent Nadeau <tanadeau at gmail.com> wrote:

> That code works fine for me if I change the cast to "as [MyProtocol]".
>
> protocol MyProtocol {}
>
> struct Blah : MyProtocol { }
>
> func foo() -> [MyProtocol] {
>   let a = [Blah(), Blah()] as [MyProtocol]
>   return a
> }
>
> On Mon, Jan 25, 2016 at 10:47 PM, Austin Zheng via swift-users <
> swift-users at swift.org> wrote:
>
>> Hi Ryan,
>>
>> Are you sure it works with user-defined struct types? I tried the
>> following code, and got the same error:
>>
>> protocol MyProtocol {}
>>
>> struct Blah : MyProtocol { }
>>
>> func foo() -> [MyProtocol] {
>>   let a = [Blah(), Blah()] as [Blah]
>>   return a
>> }
>>
>> 'class Blah' works fine.
>>
>> Even so, this is not the behavior I would have expected. Perhaps someone
>> else can explain why [T] can't be upcasted to [P] when T is a struct and T
>> : P.
>>
>> Best,
>> Austin
>>
>>
>> On Jan 25, 2016, at 7:36 PM, Ryan Walklin via swift-users <
>> swift-users at swift.org> wrote:
>>
>> Hi All,
>>
>> I have a function which returns a closure, which then returns an array of
>> objects conforming to a protocol.
>>
>> ie.
>>
>> protocol MyProtocol {}
>>
>> extension Float: MyProtocol {}
>> extension OtherType: MyProtocol {}
>>
>> When I try to return an array of Floats, I get the error “Cannot convert
>> value of type '[Float]' to closure result type ‘[MyProtocol]”.
>>
>> Other struct-based types work fine.
>>
>> Is this not possible with standard library types?
>>
>> Regards,
>>
>> Ryan
>> _______________________________________________
>> swift-users mailing list
>> swift-users at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-users
>>
>>
>>
>> _______________________________________________
>> swift-users mailing list
>> swift-users at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-users
>>
>>
>
>
> --
> Trent Nadeau
>



-- 
Trent Nadeau
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-users/attachments/20160125/617e104c/attachment.html>