Extend array types using where clause in Swift

Question

I'd like to use the Accelerate framework to extend [Float] and [Double] but each of these requires a different implementation.

I tried the obvious:

extension Array<Float> { } 

and get this error:

"Constrained extension must be declared on the unspecialised generic type 'Array' with constraints specified by a 'where' clause"

Is it posible to extend generic types in Swift 2 in this way?

I've got the code working as expected now. Here's an example showing a summation using the Accelerate framework.

extension _ArrayType where Generator.Element == Float {      func quickSum() -> Float {         var result: Float = 0         if var x = self as? [Float] {             vDSP_sve(&x, 1, &result, vDSP_Length(x.count))         }         return result     } }  extension _ArrayType where Generator.Element == Double {      func quickSum() -> Double {         var result: Double = 0         if var x = self as? [Double] {             vDSP_sveD(&x, 1, &result, vDSP_Length(x.count))         }         return result     } } 

Answer 1

If you want to extend only array with specific type. You should extend _ArrayType protocol.

extension _ArrayType where Generator.Element == Int {     func doSomething() {        ...     } } 

If you extend Array you can only make sure your element is conformed some protocol else. i.e:

extension Array where Element: Equatable {     func doSomething() {        ...     } } 

Updated: With Swift 3.1 https://github.com/apple/swift/blob/master/CHANGELOG.md

extension Array where Element == Int {     func doSomething() {        ...     } } 

Answer 2

Swift 3 to the rescue!!

extension Collection where Iterator.Element == Int {     // `Collection` can be `Sequence`, etc }