Re: What's polymorphic in CRTP
On 02/11/13, Jarek Blakarz wrote:
Hi
I understand what is CRTP. What I don't understand is why CRTP is called a
static polymorphism or rather polymorphism in particular.
Never heard of this though I have used CRTP lots of times. Most
textbooks make a difference between static and dynamic polymorphism with
regard to whether the polymorphic behaviour is resolved at compile time
or run-time. The classic example for static polymorphism is function
overloading. Although, the term may also be applied to CRTP, I guess.
I think that it is "static" since the function call is resolved at compile
time, right ?
I'd say right.
Assuming that I'm right about "static", plese explain me based on the following
example why it is "polymorphic".
thanks for clarification.
template <class Derived> struct Base {
void interface() { static_cast<Derived*>(this)->implementation(); }
At this place the writer of this code cannot tell which implementation
of the invoked member function "implementation" will be called, so one
could say that the invokation of the "implementation" method on the
"this" pointer is polymorphic behaviour.
I don't like the term "static polymorphism" very much. In my opinion
"polymorphism" and "static" contradict each other. But apparently most
scientist from "applied computer science" (another contradiction?) think
otherwise.
};
struct Derived1 : Base<Derived1> {
void implementation() { }
};
struct Derived2 : Base<Derived2> {
void implementation() { }
};
Derived1 *d1 = new Derived1;
Derived2 *d2 = new Derived2;
d1->interface();
d2->interface();
Regards,
Stuart