Java interface equivalent in Swift [duplicate]

Question

EDIT: What is different between What is the equivalent for java interfaces or objective c protocols in swift? and this question?

After I read that topic, I thought It was an option to use a class to extend the protocol, and I tried to create the protocol itself with no success, but as Duncan C. said it is not possible to initialise a protocol type directly and I have to extend it with another class.

My Problem: I have a class in Java, I hold an array of interfaces, that way I can loop through the array and call the doWork() function until one of them returns true. I want to achieve the same functionality in Swift.

My java class:

class MyClass{
    //create a variable that holds all of my engines
    private MyEngine[] myEngines = new MyEngine[]{
        new MyEngine(){
            @Override
            public boolean doWork(){
                return doWork1();
            }        
        },
        new MyEngine(){
            @Override
            public boolean doWork(){
                return doWork2();
            }        
        },
        new MyEngine(){
            @Override
            public boolean doWork(){
                return doWork3();
            }        
        }
    }

    //loop through all engines until one of them succeed
    public boolean doWorkUntilSuccess(){
        for(int i = 0; i < myEngines.length; i++){
            if(myEngines[i].doWork())
                return true;
        }
        return false;
    }

    private boolean doWork1(){
        //code
        return result;
    }

    private boolean doWork2(){
        //code
        return result;
    }

    private boolean doWork3(){
        //code
        return result;
    }

    interface MyEngine{
        boolean doWork();
    }
}

Answer 1

The Swift equivalent to an interface is a Protocol, as Connor says in his answer.

Again, borrowing from Connor's answer:

protocol MyEngine {
    func doWork() -> Bool
}

You can't instantiate objects of type MyEngine directly. Instead you need to define one or more objects that conform to the protocol:

class Obj1: MyEngine {
    func doWork() -> Bool {
        print("in Obj1 doWork()")
        return true
    }
}

class Obj2: MyEngine {
    func doWork() -> Bool {
        print("in Obj2 doWork()")
        return true
    }
}

You can then define an array of objects that conform to the protocol:

var objArray = [MyEngine]()

Then populate the array:

objArray.append(Obj1())
objArray.append(Obj2())
objArray.append(Obj2())
objArray.append(Obj1())

You can then say

objArray.forEach{$0.doWork()}

Answer 2

What you're looking for is a protocol.

protocol MyEngine {
    func doWork() -> Bool
}

Classes can then implement the protocol. However, there is no equivalent (to my knowledge) of saying new MyEngine(). You need to declare a class or struct that implements the protocol.