Composing A Protocol

Contents.swift

protocol BaseDelegate: class {
    func baseMethod()
}

protocol SecondaryDelegate: BaseDelegate {
    func secondaryMethod()
}

protocol TertiaryDelegate: BaseDelegate {
    func tertiaryMethod()
}


class SomethingWithDelegate {
    
    var baseDelegate: BaseDelegate
    
    init(baseDelegate: BaseDelegate) {
        self.baseDelegate = baseDelegate
    }
    
    func runTheMethods() {
        self.baseDelegate.baseMethod()
        
        if let secondary = self.baseDelegate as? SecondaryDelegate {
            secondary.secondaryMethod()
        }
        
        if let tertiary = self.baseDelegate as? TertiaryDelegate {
            tertiary.tertiaryMethod()
        }
    }
}

class ConformsToBase: BaseDelegate {
    
    func baseMethod() {
        print("I only conform to the base method")
    }
}

class ConformsToSecondary: SecondaryDelegate {
    func secondaryMethod() {
        print("I conform to secondary as well!")
    }
    
    func baseMethod() {
        print("I conform to base and...")
    }
}

class ConformsToTertiary: TertiaryDelegate {
    
    func baseMethod() {
        print("I conform to base and...")
    }
    
    func tertiaryMethod() {
        print("I conform to tertiary as well!")
    }
}

class ConformsToAll: SecondaryDelegate, TertiaryDelegate {
    
    func baseMethod() {
        print("I conform to base and...")
    }
    func secondaryMethod() {
        print("I also conform to secondary and...")
    }
    
    func tertiaryMethod() {
        print("I also conform to tertiary!")
    }
}


let thing1 = SomethingWithDelegate(baseDelegate: ConformsToBase())
print("=== THING 1 ===")
thing1.runTheMethods()

let thing2 = SomethingWithDelegate(baseDelegate: ConformsToSecondary())
print("=== THING 2 ===")
thing2.runTheMethods()

let thing3 = SomethingWithDelegate(baseDelegate: ConformsToTertiary())
print("=== THING 3 ===")
thing3.runTheMethods()

let thing4 = SomethingWithDelegate(baseDelegate: ConformsToAll())
print("=== THING 4 ===")
thing4.runTheMethods()

output.txt

=== THING 1 ===
I only conform to the base method
=== THING 2 ===
I conform to base and...
I conform to secondary as well!
=== THING 3 ===
I conform to base and...
I conform to tertiary as well!
=== THING 4 ===
I conform to base and...
I also conform to secondary and...
I also conform to tertiary!

I was pretty convinced this was not possible without @objc but I am happy to be proven wrong!