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Thread: [C++] Double Dispatch

  1. #1
    Sergeant serthy's Avatar
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    [C++] Double Dispatch

    PHP Code:
    #include <iostream>

    //forward declerations of derived classes
    class Sphere;
    class 
    Box;

    class 
    Volume //my base class
    {
        public:

            
    //virtual, non-base-class methods
            
    virtual void checkCollision( const Volume) const = 0;
            
    virtual void checkCollision( const Sphere) const = 0;
            
    virtual void checkCollision( const Box) const = 0;
    }

    class 
    Sphere : public Volume //derived 1
    {
        public:

            
    void checkCollision( const Volume) const
            {
                
    std::cout << "redo: sphere vs volume" << std::endl;

                return 
    v.checkCollision( *this );
            }

            
    void checkCollision( const Sphere) const
            {
                
    std::cout << "sphere vs sphere" << std::endl;
            }

            
    void checkCollision( const Box) const
            {
                
    std::cout << "sphere vs box" << std::endl;
            }
    }

    class 
    Box : public Volume //derived 2
    {
        public:

            
    void checkCollision( const Volume) const
            {
                
    std::cout << "redo: box vs volume" << std::endl;

                return 
    v.checkCollision( *this );
            }

            
    void checkCollision( const Sphere) const
            {
                
    std::cout << "box vs sphere" << std::endl;
            }

            
    void checkCollision( const Box) const
            {
                
    std::cout << "box vs box" << std::endl;
            }
    }

    int mainint argCount charargs[] )
    {
        
    Volume v;
        
    Sphere s;
        
    Box b;

        
    //doesnt work, because of virtual = 0; methods in base class, comment them out then
        
    std::cout << "VOLUME:" << std::endl;

        
    v.checkCollision);
        
    v.checkCollision);
        
    v.checkCollision);

        
    std::cout << "SPHERE:" << std::endl;

        
    s.checkCollision);
        
    s.checkCollision);
        
    s.checkCollision);

        
    std::cout << "BOX:" << std::endl;

        
    b.checkCollision);
        
    b.checkCollision);
        
    b.checkCollision);

    My understanding of double dispatch, is there an easier and maybe more dynamic method (for adding new derived classes?) without any casting methods?
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  2. #2
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    Quote Originally Posted by serthy View Post
    PHP Code:
    #include <iostream>

    //forward declerations of derived classes
    class Sphere;
    class 
    Box;

    class 
    Volume //my base class
    {
        public:

            
    //virtual, non-base-class methods
            
    virtual void checkCollision( const Volume) const = 0;
            
    virtual void checkCollision( const Sphere) const = 0;
            
    virtual void checkCollision( const Box) const = 0;
    }

    class 
    Sphere : public Volume //derived 1
    {
        public:

            
    void checkCollision( const Volume) const
            {
                
    std::cout << "redo: sphere vs volume" << std::endl;

                return 
    v.checkCollision( *this );
            }

            
    void checkCollision( const Sphere) const
            {
                
    std::cout << "sphere vs sphere" << std::endl;
            }

            
    void checkCollision( const Box) const
            {
                
    std::cout << "sphere vs box" << std::endl;
            }
    }

    class 
    Box : public Volume //derived 2
    {
        public:

            
    void checkCollision( const Volume) const
            {
                
    std::cout << "redo: box vs volume" << std::endl;

                return 
    v.checkCollision( *this );
            }

            
    void checkCollision( const Sphere) const
            {
                
    std::cout << "box vs sphere" << std::endl;
            }

            
    void checkCollision( const Box) const
            {
                
    std::cout << "box vs box" << std::endl;
            }
    }

    int mainint argCount charargs[] )
    {
        
    Volume v;
        
    Sphere s;
        
    Box b;

        
    //doesnt work, because of virtual = 0; methods in base class, comment them out then
        
    std::cout << "VOLUME:" << std::endl;

        
    v.checkCollision);
        
    v.checkCollision);
        
    v.checkCollision);

        
    std::cout << "SPHERE:" << std::endl;

        
    s.checkCollision);
        
    s.checkCollision);
        
    s.checkCollision);

        
    std::cout << "BOX:" << std::endl;

        
    b.checkCollision);
        
    b.checkCollision);
        
    b.checkCollision);

    My understanding of double dispatch, is there an easier and maybe more dynamic method (for adding new derived classes?) without any casting methods?
    You can get the double dispatch code link here : https://gist.github.com/s3rvac/ddb2a0ffc6bcc1d3b2f6
    Without type cast.

  3. #3
    Assadministrator kung foo man's Avatar
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    How about using a proper programming language https://en.wikipedia.org/wiki/Multiple_dispatch#Julia
    timescale 0.01

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