[swift-evolution] Pitch: Allow generic functions to fulfill non-generic protocol requirements

Xiaodi Wu xiaodi.wu at gmail.com
Wed May 24 19:52:30 CDT 2017

On Wed, May 24, 2017 at 7:21 PM, David Sweeris <davesweeris at mac.com> wrote:

> On May 24, 2017, at 5:11 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> On Wed, May 24, 2017 at 3:32 PM, David Sweeris via swift-evolution <
> swift-evolution at swift.org> wrote:
>> So, I’m working on a type, and would like to make it conform to
>> `ExpressibleByArrayLiteral`. The thing is, I don’t actually care what type
>> `Element` is as long as it conforms to `FixedWidthInteger` and
>> `UnsignedInteger`. I tried writing this:
>>   public init <U: FixedWidthInteger & UnsignedInteger> (arrayLiteral
>> elements: U...) { … }
>> But Xcode says my type doesn’t conform to `ExpressibleByArrayLiteral`
>> unless I add an init that takes a concrete type:
>>   public init(arrayLiteral elements: UInt...) { … }
>> Does anyone else think the generic init should to be able to satisfy
>> `ExpressibleByArrayLiteral` (especially since `UInt` meets the conformance
>> requirements)?
> Your type needs to be generic.
> It already is… I just don’t want to restrict it to being initialized from
> array literals containing that same generic type.

Not sure of your particular use case, but it sounds like you'd want to
write a type-erased AnyFixedWidthUnsignedInteger wrapper.
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