Swift protocol extensions

Maths.swift

protocol Raisable {
    func raise(exponent : Self) -> Self
}

extension Raisable where Self : SignedNumberType {
    func raise(exponent : Self) {
        return pow(self, exponent)
    }
}

protocol Squarable : Raisable {
    func squared() -> Self
}

extension Squarable {
    func squared() -> Self {
        return self.raise(2)
    }
}

http://stackoverflow.com/questions/31702831/swift-2-protocol-extension-using-pow/31703542#31703542