C++: Losing access to memebers of a child class when converting child into the parent

First of all this is my first post so please be gentle. :)

I have a question (perhaps quite basic) but its quite specific and I couldn't find anything that would answer it.

I have created a Shader class that is a parent of a FacingRatioShader class. In the main.cpp I create an instance of a FacingRatioShader class and I pass it as a argument to an Object::addShader(Shader _shaderType) method:

void Object::addShader(Shader &_shaderType)
{
    m_shaderType = _shaderType;
}

And in the header of Object:

Shader m_shaderType;

The problem is that once the m_shaderType has been set it becomes a Shader type instead of FacingRatioShader type. Because of this I am loosing the ability to access the FacingRatioShader specific method called compute().

Is there anyway of creating the type for m_shaderType and modifying Object::addShader so that it can accept any child of a Shader class but still keeping the possibility to access the child methods?

I hope that my question is clear enough. If not please do not hesitate to ask me for more details.

Thanks in advance!

Regads, Dawid

Solution

The answer is partly yes, and partly no. You can change m_shaderType to store a pointer, but you will still only be able to call methods that are declared inside the parent class (so in Shader).

If you want to call methods dependant on the class/subclass, declare them in the base class as virtual and overwrite their bodies inside child classes.

class Object{
   Shader* m_shaderType;
   // ...
   void addShader(Shader &_shaderType)
   {
      m_shaderType = &_shaderType;
   }
   // ...
};

You could - theoretically - store information about what type did you pass to addShader (with an additional variable that you would set accordingly to recognize the child classes), but that's not a really good idea.