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>{};

Example

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 <cstdio>   #ifndef __cpp_explicit_this_parameter // Traditional syntax   template<class Derived>struct Base {void name(){static_cast<Derived*>(this)->impl();}protected: Base()=default;// prohibits the creation of Base objects, which is UB};struct D1 :public Base<D1>{void impl(){std::puts("D1::impl()");}};struct D2 :public Base<D2>{void impl(){std::puts("D2::impl()");}};   #else // C++23 deducing-this syntax   struct Base {void name(this auto&& self){ self.impl();}};struct D1 :public Base {void impl(){std::puts("D1::impl()");}};struct D2 :public Base {void impl(){std::puts("D2::impl()");}};   #endif   int main(){ D1 d1; d1.name(); D2 d2; d2.name();}

Output:

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

See also

Explicit object member functions (deducing this)(C++23)
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)

External links

1.	Replace CRTP with concepts? — Sandor Drago's blog
2.	The Curiously Recurring Template Pattern (CRTP) — Sandor Drago's blog
3.	The Curiously Recurring Template Pattern (CRTP) - 1 — Fluent{C++}
4.	What the CRTP can bring to your code - 2 — Fluent{C++}
5.	An implementation helper for the CRTP - 3 — Fluent{C++}
6.	What is the Curiously Recurring Template Pattern (CRTP) — SO