ProtocolAbstraction.swift

import UIKit

var str = "Hello, playground"

protocol A {
    func hello()
}

protocol B: A {
    func hello2()
}


class AA: A {
    func hello() {
        print("AA")
    }
    
    
}
class BB: AA, B {
    func hello2() {
        print("BB")
    }
    
    
}


let b: B = BB()
//b.hello2()
//b.hello()

let a: A? = b
a?.hello()