Adrian,
thanks, but don’t work :-(
import Foundation
protocol AreaProtocol {
// required
func area() -> CGFloat
// implemented in protocol extension
func volume( height:CGFloat ) -> CGFloat
// ....
}
extension AreaProtocol {
func volume( height:CGFloat ) -> CGFloat {
return height * area()
}
// ....
// ....
}
protocol CGPointSequence: Sequence, AreaProtocol where Element == CGPoint {}
extension CGPointSequence {
func area() -> CGFloat {
return 0.0 // ... poligon area
}
}
extension Array:CGPointSequence {} // !'CGPointSequence' requires the types
'Element' and 'CGPoint' be equivalent
> Il giorno 25 nov 2017, alle ore 09:11, Adrian Zubarev
> <[email protected]> ha scritto:
>
> This is correct. None of your types does conform to your protocol because you
> never conformance explicitly.
>
> The extenstion you wrote is just a conditional extension which says if the
> Self type conforms to AreaProtocol and the associated typed Element is a
> CGPoint then add the area method to it. Nothing more, nothing less.
>
> Now you may think that you have to rewrite that extension to `extension
> Sequence : AreaProtocol where Element == CGPoint`, but that won't work
> because retroactively conforming protocols to other protocols is not
> supported yet. Nor are conditional conformances included yet, but they will
> in Swift 4.1 or 5.
>
> You have one option left.
> protocol MySequence : Sequence, AreaProtocol where Element == CGPoint {}
>
> extension Array : MySequence {}
>
> Then also conform other sequences you need to support that functionality.
>
> Double check if the code compiles, I wrote it on my iPhone, but you get the
> idea now.
>
> --
> Adrian Zubarev
> Sent with Airmail
> Am 25. November 2017 um 07:40:25, Antonino Ficarra via swift-users
> ([email protected] <mailto:[email protected]>) schrieb:
>
>> In this code example:
>>
>> import Foundation
>>
>> protocol AreaProtocol {
>> func area() -> CGFloat
>>
>> // implemented in protocol extension
>> func volume( height:CGFloat ) -> CGFloat
>> // ....
>> }
>>
>> extension AreaProtocol {
>> func volume( height:CGFloat ) -> CGFloat {
>> return height * area()
>> }
>> // ....
>> // ....
>> }
>>
>>
>> // conform CGPoint sequences to AreaProtocol
>> extension Sequence
>> where Self : AreaProtocol, Element == CGPoint
>> {
>> func area() -> CGFloat {
>> return 0.0 // ... poligon area
>> }
>> }
>>
>> let p0 = CGPoint(x: 0.0, y: 0.0)
>> let p1 = CGPoint(x: 2.0, y: 0.0)
>> let p2 = CGPoint(x: 2.0, y: 2.0)
>> let p3 = CGPoint(x: 0.0, y: 2.0)
>>
>> let poligon = [p0,p1,p2,p3]
>> let a = poligon.area()// ! Type '[CGPoint]' does not conform to protocol
>> 'AreaProtocol'
>> let v = poligon.volume( height:10.0 )// ! Value of type '[CGPoint]' has no
>> member 'volume'
>>
>>
>> An array of CGPoint is a CGPoint sequence? Why the array don't gets
>> automatic conformance to AreaProtocol?
>> How can conform an array of CGPoint to AreaProtocol?
>>
>> Sorry for my bad english,
>> Antonino
>>
>> _______________________________________________
>> swift-users mailing list
>> [email protected]
>> https://lists.swift.org/mailman/listinfo/swift-users
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