Composite.swift

protocol Component {
    
    func foo()
}

class Composite: Component {
    
    var children: [Component] = []
    
    func foo() {
        for child in children {
            child.foo()
        }
    }
}

class LeafA: Component {
    
    func foo() {
        print("Hi, I'm Leaf A")
    }
}

class LeafB: Component {
    
    func foo() {
        print("Hi, I'm Leaf B")
    }
}


let composite = Composite()
composite.children = [ LeafA(), LeafB() ]
composite.foo()

// Hi, I'm Leaf A
// Hi, I'm Leaf B