CRTP vs virtual function example.

CRTP.cpp

#include<iostream>

using namespace std;


template<typename Derived>  class Parent 
{
public:
    void SayHi()
    {
        static_cast<Derived*>(this)->SayHiImpl();
    }
private:
    void SayHiImpl()
    {
        cout << "hi, i'm default!" << endl;
    }
};

class ChildA :public Parent<ChildA>
{
public:
    void SayHiImpl()
    {
        cout << "hi, i'm child A!" << endl;
    }
};

class ChildB :public Parent<ChildB>
{
};



class ParentB
{
public:
    void virtual SayHi()
    {
        cout << "hi, i'm default!" << endl;
    }
};

class ChildC : public ParentB
{
public:
    void SayHi()
    {
        cout << "hi, i'm ChildC!" << endl;
    }
};

class ChildD : public ParentB
{
}; 


template<typename Derived> void CRTP(Parent<Derived>& p)
{
    p.SayHi();
}

void Dynamic(ParentB& p)
{
    p.SayHi();
}

int _tmain(int argc, TCHAR* argv[])
{

    ChildA a;
    CRTP(a);
    cout << "size of ChildA: " << sizeof(a) << endl;

    ChildB b;
    CRTP(b);
    cout << "size of ChildB: " << sizeof(b) << endl;

    ChildC c;
    Dynamic(c);
    cout << "size of ChildC: " << sizeof(c) << endl;

    ChildD d;
    Dynamic(d);
    cout << "size of ChildD: " << sizeof(d) << endl;

    return 0;
}