some crtp base class #cpp #c++ #crtp

crtp.cpp

#include <type_traits>
#include <utility>

template <typename Derived>
struct Crtp {
protected:
  inline Derived& derived() & noexcept { 
      return *static_cast< Derived* >(this); 
  }
  inline const Derived& derived() const & noexcept {
      return *static_cast< const Derived* >(this);
  }
  inline Derived&& derived() && noexcept { 
      return std::move(*static_cast< Derived* >(this));
  }
};

struct Foo : Crtp<Foo>
{
  using Crtp<Foo>::derived;
};

int main() {
  
  Foo foo_a;
  const Foo foo_b;

  static_assert(std::is_same<Foo&, decltype(foo_a.derived())>::value, "nop");
  static_assert(std::is_same<const Foo&, decltype(foo_b.derived())>::value, "nop");
  static_assert(std::is_same<Foo&&, decltype(Foo().derived())>::value, "nop");
}