[swift-evolution] [Discussion] Additional generics specialization

[Adrian Zubarev]

I wasn’t asking to get something like this now. I was curios and I don’t feel like curios question like this should be asked in the user mail-list. Maybe we need an extra mail-list for discussion and this will only remain for proposals and review, which will sort out such additional topics and don’t bother the review process.

After I posted the question I realized myself that the given example will only work for generics with a single inner type.

That’s why you’re totally right about the ability without specialization. :)

The next problem you’re design, that it does not work with structs and enums.



-- 
Adrian Zubarev
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Am 18. Juli 2016 um 09:17:44, Charlie Monroe (charlie at charliemonroe.net) schrieb:

In general, Swift will need a way to point to a generic type without a particular specialization. Currently, you can't do this:

class APICall<T> { }

class CombinedCall: APICall<Bool> {
var calls: [APICall] // Error - no specialization
}

I've been currently working around this by:

class APICallBase {} // No generics
class APICall<T>: APICallBase {}
class CombinedCall: APICall<Bool> {
var calls: [APICallBase]
}

But it's definitely a pain to work with.

As asked by the core team several times now, we should defer any discussion on additional features until August.


On Jul 18, 2016, at 9:04 AM, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:

This is something additional, but I’m curios about how the community feels about it.

I recently come across the issue where conforming to Hashable wasn’t enough to thecke if two instances of the same generic type were equal.

I had additionally provide myself the != function.

public func !=<T, U>(lhs: SomeTypeName<T>, rhs: SomeTypeName<U>) -> Bool {
    return lhs.hashValue != rhs.hashValue
}
I wondered if Swift can ever get generic specialization like this:

public func !=<T : Hashable, U, V>(lhs: T<U>, rhs: T<V>) -> Bool {
    return !(lhs.hashValue == rhs.hashValue)
}
This function in stdlib would fill the gap. Or we need an extra protocol GenericHashable which includes !=.




-- 
Adrian Zubarev
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