Re: What's polymorphic in CRTP
On 02/15/2013 12:01 PM, Jarek Blakarz wrote:
Thanks for the reply to all of you.
I spent some time looking at Windows examples but it seems to complex to me at
the beginning.
Could you please give me a simple example of CRTP as a replacement for dynamic
polymorphism. In case of dynamic polymorphism it seems quite obvious to me why
it is powerful. In case of CRTP I still don't feel how it can replace dynamic
polymorphism.
In case of dynamic polymorphism I can refer to the derived classes using
exactly the same interface e.g:
void fun ( Base &base )
{
base.makeSound(); // exactly the same interface for distinct derived classes
}
Unfortunately I cannot apply the same logic to CRTP static polymorphism.
In my initial example above the interface is not "exactly" the same. It is
only "similar". It differs with object name. In case of dynamic polymorphism
whenever I inherit from the base class the interface remains the same. In case
of CRTP static polymorphism whenever I inherit from the base class the
interface changes.
Thanks for the explanation.
How about this?
#include <iostream>
template<class T>
class Base {
public:
void callDynamic()
{
onDynamic();
}
void callStatic()
{
T* pThis = static_cast<T*>(this);
pThis->onStatic();
}
virtual void onDynamic()
{
std::cout << "Base::onDynamic" << std::endl;
}
void onStatic()
{
std::cout << "Base::onStatic" << std::endl;
}
};
class Derived: public Base<Derived> {
public:
virtual void onDynamic()
{
std::cout << "Derived::onDynamic" << std::endl;
}
// "pseudo virtual" function :-)
void onStatic()
{
std::cout << "Derived::onStatic" << std::endl;
}
};
int main(int, char**)
{
Derived derived;
derived.callDynamic();
derived.callStatic();
}
Also, try commenting out functions in Derived class to see what happens
Regards
--
Cholo Lennon
Bs.As.
ARG