How to simulate virtuality for method template

Question

I have a class hierarchy where I want to introduce a method template that would behave like if it was virtual. For example a simple hierarchy:

class A {
  vi         


        

Answer 1

You can use the "Curiously Recurring Template Pattern" http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern

Using this pattern, the base class takes the derived class type as a template parameter, meaning that the base class can cast itself to the derived type in order to call functions in the derived class. It's a sort of compile time implementation of virtual functions, with the added benefit of not having to do a virtual function call.

template
class A {
public:
    virtual ~A() {}

    template
    void method(T &t) { static_cast(*this).methodImpl(t); }
};

class B : public A
{
friend class A;

public:
    virtual ~B() {}

private:
    template
    void methodImpl(T &t) {}
};

It can then be used like this...

int one = 1;
A *a = new B();
a->method(one);