CODEWITHSUNDEEP
c++
Sharpie
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Reputation: 135

Copy Pointers of Object into New Pointer of this Object

I have a class, GameObject, which has a std::vector<Component*> mComponents and I have overloaded the GameObject(const GameObject&). I am trying to copy the mComponents over from one to the other, but making each of the contained Component*'s into a new object entirely, but keeping the objects contents exactly the same. This is what I have at the moment:

GameObject.cpp

GameObject::GameObject(const GameObject& other) 
{
    if (this != &other)
    {
        this->mComponents = other.mComponents; // EDIT 1
        for (int i = 0; i < (int)mComponents.size(); i++)
        {
            // FILL this->mComponents with NEW objects but
            // containing the exact same data and 
            // variables from other.mComponents
            this->mComponents[i] = other.Copy(); // EDIT 2 EXAMPLE OF IDEA IN COMMENTS
            this->mComponents[i]->setParent(this);
        }
    }
}

Engine.cpp (Extract)

GameObject cube, cube2;

cube.addComponent(new DirectionalLight(glm::vec3(-0.2f, -1.0f, -0.3f)));
cube.addComponent(new Texture("Resources/Textures/container.png", "Resources/Textures/container_specular.png"));
cube.addComponent(new Shader("Resources/Shaders/cube.shader"));
cube.addComponent(new Cube());

cube2 = GameObject(cube);

When I instantiate cube2, the mComponents Components* contents all stay exactly the same but I would like to create a new Component*'s to fill this std::vector from the GameObject(const GameObject&) fucntion, whilst keeping all the variables the same.

P.s. I know that most other operators such as '=' will not create new Components for inside the vector but I will be implementing that aswell after I figure out how to fill the vector with new Component*'s.

Upvotes: 0

Views: 89

Answers (1)

Ian Young
Ian Young

Reputation: 1746

this->mComponents[i]->Copy(other); Will not work. At least, not from a pure inheritance standpoint. A supertype (base) type pointer cannot be implicitly cast to a derived type. This is called downcasting, and no language supports it implicitly.

A simpler way to do it is to define a virtual "clone" function in each component:

virtual Component* clone()=0; // base declaration

virtual Component* Texture::clone() //derived implementation
{
    return new Texture(*this);
}

Then in your game object copy constructor:

    for (int i = 0; i < (int)other.mComponents.size(); i++)
    {
        // FILL this->mComponents with NEW objects but
        // containing the exact same data and 
        // variables from other.mComponents
        this->mComponents.push_back(other.mComponents->clone());
        this->mComponents[i]->setParent(this);
    }

This way, you let the component itself handle the copying process.

Upvotes: 4

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