simplifies the creation of non-const member functions that defer to their const member function counterparts

defer member func.cpp

#include <type_traits>

//

template <class T>
struct remove_qualifiers
: std::remove_cv<T>
{};

template <class T>
using remove_qualifiers_t = typename remove_qualifiers<T>::type;

template <class T>
struct remove_qualifiers<T&>
: std::add_lvalue_reference<remove_qualifiers_t<std::remove_cv_t<T>>>
{};
template <class T>
struct remove_qualifiers<T&&>
: std::add_rvalue_reference<remove_qualifiers_t<std::remove_cv_t<T>>>
{};
template <class T> 
struct remove_qualifiers<T*>
: std::add_pointer<remove_qualifiers_t<std::remove_cv_t<T>>>
{};

//

#define DEFER_MEMBER_FUNC(func) \
template <class... Ts> \
decltype(auto) constexpr func(Ts&&... args) \
noexcept(noexcept \
( \
    const_cast<std::remove_pointer_t<decltype(this)> const *>(this) \
    ->func(static_cast<Ts&&>(args)...)) \
) \
{ \
    using obj_t = std::remove_pointer_t<decltype(this)> const *; \
    auto const self = const_cast<obj_t>(this); \
    decltype(auto) ret = self->func(static_cast<Ts&&>(args)...); \
    return const_cast<remove_qualifiers_t<decltype(ret)>>(ret); \
}

struct faz
{
    auto constexpr& operator[](std::size_t const i) const noexcept
    { return data_[i]; }
    DEFER_MEMBER_FUNC(operator[]);

    char data_[10] = {};
};

//

auto main() -> int
{
    auto test = faz{};
    test[0] = 5;
    return test[0];    
}