Calling a child function from a parent constant object

Question

There is a simple version of my code :

   class Action:
        {
        int updateOK() {
            std::cout << "" << std::endl;
            return 0;
        }
   }
   class Attack:public Action
        {
        int updateOK() {
            std::cout << "att" << std::endl;
            return 0;
        }
   }
   class Def:public Action
        {
        int updateOK() {
            std::cout << "DEf" << std::endl;
            return 0;
        }
    }

    namespace actions
    {
        const Attack light = Attack();
        const Attack meduim = Attack();
        const Attack heavy = Attack();
        const Block block = Block();
        const Block cancelBlock = Block();
        const std::vector<Action> listAction = { light , meduim, heavy , block, cancelBlock };
    }

    Main.cpp :
    for each (Action action in actions::listAction) {
                action.updateOK();
    }

The issue is that it always calls the parent function in the main.

I have tried virtual functions in many ways but I want to find a solution to the problem without casts.

Is it possible ?

You need to revisit [how polymorphism works](http://www.tutorialspoint.com/cplusplus/cpp_polymorphism.htm) — NathanOliver, Apr 12 '16 at 12:10
What do you mean without casts? Adding `virtual ` before parent function seems to be the way to go without major changes. — aybassiouny, Apr 12 '16 at 12:12
@aybassiouny Well you also need to use pointers and when you use them you will get implicit cast from the derived class to the base class pointer. — NathanOliver, Apr 12 '16 at 12:14
So I have to make a list of pointers like const std::vector listAction — Moran Abadie, Apr 12 '16 at 12:19
@NathanOliver oh you are correct I didn't read the rest of his example. If he needs a generic container he will need to use pointers to base class as objects. — aybassiouny, Apr 12 '16 at 12:20
@MoranAbadie I don't see any way around it, yes. You will also need to make the rest such as `Action* block = new Block();` — aybassiouny, Apr 12 '16 at 12:22
You should also add `;` after your class definitions, this code does not compile... — Chiel, Apr 12 '16 at 12:23

score 0 · Answer 1 · answered Apr 12 '16 at 12:24

0

what you are trying to do is Object slicing:

It happens when a derived class object is assigned to a base class object, additional attributes of a derived class object are sliced off to form the base class object

answered Apr 12 '16 at 12:24

Abhishek Chandel

1,294
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thanks I will google it ;) – Moran Abadie Apr 12 '16 at 12:26
if you want to achieve the desired result, use polymorphism. – Abhishek Chandel Apr 12 '16 at 12:28

score 0 · Answer 2 · answered Apr 12 '16 at 12:28

If you don't mind casts you need to:

Make parent function virtual for dynamic binding to work
if you need to use a generic container you will need to use pointers to base class as objects.

Sample edits:

   class Action:
   {
        virtual int updateOK() {
            std::cout << "" << std::endl;
            return 0;
        }
   };

--- the rest of classes --- 

    namespace actions
    {
        const Action* light = new Attack();
        const Action* meduim = new Attack();
        const Action* heavy = new Attack();
        const Action* block = new Block();
        const Action* cancelBlock = new Block();
        const std::vector<Action*> listAction { light , meduim, heavy , block, cancelBlock };
    }

    Main.cpp :
    for(Action* action : actions::listAction) {
                action->updateOK();
    }

I tried it before but the problem is that it gave me an ` error : cannot convert from 'Action *const ' to 'Action'` — Moran Abadie, Apr 12 '16 at 13:40

Calling a child function from a parent constant object

2 Answers2