Thread: can i do instance polymorphism?

is possible do a instance polymorphism?
i understand that i can create class's with virtual functions, but i only can change them with another class and not with objects\instances

Originally Posted by laserlight

Can't be done.

even with adicional class's or precompiler code?

Originally Posted by laserlight

The effect that you have in mind can be done in standard C++, e.g., by assigning a unique id to each object and then selecting the behaviour based on this id. Why do you want to do this? Perhaps a better way can be suggested.

is for build events and change the events outside of the main function. i have the:

Code:

typedef std::function<void(void)> OnSomethingHandler;

but i can't change the values outside of the main

sorry, i mean:

Code:

#define event(eventname, ... ) std::function<void(__VA_ARGS__ )> eventname

Originally Posted by laserlight

I don't know what you mean by "build events" and I don't know exactly what you are trying to change and where. Logically though, if you have a callback function (object), you can replace it at run time.

sorry my english
but what i realy need is these:

returntype objectname::functionname()//with arguments or not

but doing outside of the main function...
sorry but i'm problems to express better but i think the MFC way, can give you a clue... i think. or the Visual C++ form applications.
they use the '::' operator for change\write the event(the windows messages are events)

Originally Posted by laserlight

That sounds simple enough: returntype would be your callback function (object) type. functionname, which probably should be renamed to something more descriptive, would just return the callback function (object). You can then set the function (object) on a per-object basis outside of the main function, at run time, and then retrieve it from the object named obj by calling obj.functionname(). I don't see a problem.

but if i use an objectname, the compiler give me errors
(i have send you a message, because theres 2 things that i don't know on forum)

Originally Posted by laserlight

Oh right, by objectname you really mean an object's name, not a class named objectname.


I am not familiar with MFC or Visual C++ form applications, but here's the thing: why does it matter that in the interface that they provide, the scope resolution operator (i.e., :: ) is used? That's just syntax; it only matters in the bigger picture of the interfaces that they provide. What's more important is what you are trying to do. So if you say that:

Code:

but what i realy need is these:

returntype objectname::functionname()//with arguments or not

then I can tell you that since what you really need is invalid C++, you need to change what you really need, or perhaps recognise that you didn't really need it to begin with. If you cannot do that, then you need to change programming language, or change the programming language.

what i know that i can do these:

Code:

#define event(eventname, ... ) std::function<void(__VA_ARGS__ )> eventname

class test
{
   public:
      event(Print)=[](){;};
};

void hello()
{
     cout << "hello world";
}

int main()
{
   test a;
   a.print=&hello;
   a.print();
  return 0;
}

it's very nice... true, but i must use 'a.print=&hello;'... unless we can do:

Code:

#define event(eventname, ... ) std::function<void(__VA_ARGS__ )> eventname

class test
{
   public:
      event(Print)=[](){;};
};

void a_hello()
{
     cout << "hello world";
}

int main()
{
   test a;
   a.print=&hello;//and the compiler do these line...(it's just a thot)
   a.print();
  return 0;
}

what you can tell me about my thot?
(sorry if i bored you with these thread, but i want something like these)