Curiously Recurring Template Pattern

 

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The Curiously Recurring Template Pattern is an idiom in which a class X derives from a class template Y, taking a template parameter Z, where Y is instantiated with Z=X. For example,

template<class Z>
class Y {};
 
class X : public Y<X> {};

CRTP may be used to implement "compile-time polymorphism", when a base class exposes an interface, and derived classes implement such interface.

Run this code

#include <iostream>
 
template <class Derived>
struct Base { void name() { (static_cast<Derived*>(this))->impl(); } };
 
struct D1 : public Base<D1> { void impl() { std::cout << "D1::impl()\n"; } };
struct D2 : public Base<D2> { void impl() { std::cout << "D2::impl()\n"; } };
 
int main()
{
    Base<D1> b1; b1.name();
    Base<D2> b2; b2.name();
 
    D1 d1; d1.name();
    D2 d2; d2.name();
}

Output:

D1::impl()
D2::impl()
D1::impl()
D2::impl()

See also

enable_shared_from_this (C++11)	allows an object to create a shared_ptr referring to itself (class template)
ranges::view_interface (C++20)	helper class template for defining a view, using the curiously recurring template pattern (class template)