[swift-evolution] [Discussion] Generic protocols

[Daniel Leping]

Guys, I think we've got quit some positive feedback for this.

Maybe it's time to go to proposal stage? I personally will back it 100%.

If there is anything to add at this stage?

On Mon, 5 Dec 2016 at 21:46 Adrian Zubarev via swift-evolution <
swift-evolution at swift.org> wrote:

> Syntactic sugar could only solve the first issue because it would create a
> generic type that allows you to reuse your protocol with associated types
> in a way like ConstructibleFromValue<Float> would.
>
> The idea is simple, but there are a few disadvantages that makes it less
> worth to implement.
> ------------------------------
>
> If I should describe it in a different way, I’d prefer something like this
> instead:
>
> typealias GenericCollection<E> = Collection where Iterator.Index == Int, Element == E
>
> //====================================//
>
> protocol ConstructibleFromValue {
>   associatedtype ValueType
>   init(_ value: ValueType)
> }
>
> typealias ConstructibleFrom<V> = ConstructibleFromValue where ValueType == V
>
> // In both cases I want to be able to conform to this macro/shortcut.
> // I don't speak about existentials here.
>
> protocol MyType {}
>
> extension MyType : ConstructibleFrom<Float> {
>     init(_ value: Float) { ... }
> }
>
> extension MyType : ConstructibleFrom<Double> {
>     init(_ value: Double) { ... }
> }
>
>
>
> --
> Adrian Zubarev
> Sent with Airmail
>
> Am 3. Dezember 2016 um 21:21:23, Xiaodi Wu (xiaodi.wu at gmail.com) schrieb:
>
> I'm not sure I understand. The first feature in the generics manifesto is
> parameterized protocols so that you can have, say, ConstructibleFrom<Float>
> and ConstructibleFrom<Int> and the ability to conform to the same protocol
> in two ways. The second feature is explained as a request for generalized
> existentials. I don't understand how syntactic sugar solves either issue.
>
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