CODEWITHSUNDEEP
swiftinheritanceprotocolsswift-protocols
Logan
Logan

Reputation: 53142

Why can't I provide default implementations for Type functions returning Self in protocol when using inheritance?

Why doesn't this work:

protocol Work {
    init()
    static func make() -> Self
}

extension Work {
    static func make() -> Self {
        return self.init()
    }
}

class Foo : Work {
    required init() {}
}

I can make inheritance possible by adding the factory to the object itself:

class Foo : Work {
    required init() {}

    static func make() -> Self {
        return self.init()
    }
}

I could also use a non-class or mark the class final, but I'd prefer/am required to use inheritance.

Is it possible to implement a default factory on a protocol so that an inheritable type can conform without implementing it again.

Upvotes: 0

Views: 49

Answers (1)

GetSwifty
GetSwifty

Reputation: 7756

If you want a factory that will initialize objects adhering to a protocol, you should use the always awesome generics! E.g.

protocol Work {
    init()
    static func make<T: Work>(type: T.Type) -> T
}

extension Work {
    static func make<T: Work>(type: T.Type) -> T {
        return T.init()
    }
    static func make() -> Self {
        return make(Self)
    }
}

class Foo : Work {
    required init() {}
}

Upvotes: 1

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