Extending typed array by conforming to a protocol in Swift 2

Question

I want to extend a typed array Array so that it conforms to a protocol SomeProtocol. Now I know you can extend a typed array like b

Answer 1

You can't apply a lot of logic to conformance. It either does or does not conform. You can however apply a little bit of logic to extensions. The code below makes it easy to set specific implementations of conformance. Which is the important part.

This is used as a typed constraint later.

class SomeType { }

This is your protocol

protocol SomeProtocol {

    func foo()

}

This is an extension of the protocol. The implementation of foo() in an extension of SomeProtocol creates a default.

extension SomeProtocol {

    func foo() {
        print("general")
    }
}

Now Array conforms to SomeProtocol using the default implementation of foo(). All arrays will now have foo() as a method, which is not super elegant. But it doesn't do anything, so it's not hurting anyone.

extension Array : SomeProtocol {}

Now the cool stuff: If we create an extension to Array with a type constraint for Element we can override the default implementation of foo()

extension Array where Element : SomeType {
    func foo() {
        print("specific")
    }
}

Tests:

let arrayOfInt = [1,2,3]
arrayOfInt.foo() // prints "general"

let arrayOfSome = [SomeType()]
arrayOfSome.foo() // prints "specific"