c++ Type confusion stopper. A.k.a -- Reduce compound type to base type

dbj_type_reductor.h

// (c) 2019/2020 by [email protected] 
// CC BY SA 4.0
//
// https://wandbox.org/permlink/h8BE47pvLlBMy7wy
// clang++ prog.cc -std=c++14
// OK for C++14, C++17, C++2a
//
// https://dbj.org/c-reduce-compound-to-base-type/
//
#include <iostream>
#include <string>

namespace dbj 
{
    #if __cplusplus < 201703L
    // for C++14
    // inline variables are a C++17 extension too
    template< class T, class U >
      static constexpr bool is_same_v = std::is_same<T, U>::value;
    #endif
	
    template <typename T> struct remove_all_ptr { typedef T type;	};

	template <typename T> struct remove_all_ptr<T*>	{
		using type = typename remove_all_ptr<std::remove_cv_t<T>>::type;
	};
    
    template <typename T>
    using remove_all_ptr_t = typename remove_all_ptr<T>::type ;
    
template< class T >
struct remove_cvref {
	typedef std::remove_cv_t<std::remove_reference_t<T>> type;
};

template< class T >
using remove_cvref_t = typename remove_cvref<T>::type;

template <class T>
using to_base_t =
  remove_all_ptr_t< std::remove_all_extents_t< remove_cvref_t < T > > >;
    
} // dbj

//////////////////////////////////////////////////////////////////////////////////////
//
// use cases are the proof of usefulness
// feel free to add your own
//
//////////////////////////////////////////////////////////////////////////////////////

    // char is base type, deduced from six levels of pointers to char
	static_assert(dbj::is_same_v<char ,dbj::to_base_t<char ******>>, "Failed!" );

    // std::string is base type for array of pointers to std::string
	static_assert(dbj::is_same_v<std::string ,dbj::to_base_t<std::string * (&)[]>>, "Failed!" );

    // void () function
	static_assert(dbj::is_same_v<void (), dbj::to_base_t<void ()>>, "Failed!") ;
    
    struct X { char data{}; char method () const { return {};} };
    // base type is X for an reference to array of X
	static_assert(dbj::is_same_v<X, dbj::to_base_t<X (&) []>>, "Failed!" );
    
    // pointer to method on X 
    using method_t = char (X::*)() ;
    // base type is that metod, deduced from an ref to the array of nethod pointers
	static_assert(dbj::is_same_v<method_t, dbj::to_base_t< method_t (&) []>>, "Failed!" );

int main( int argc, char ** argv )
{
    return 1;
}