add dependent_false

[gpeterhoff]

always false idiome
dependent_false.hpp

//	Distributed under the Boost Software License Version 1.0 https://www.boost.org/LICENSE_1_0.txt
//	Copyright Gero Peterhoff

#ifndef BOOST_TYPE_TRAITS_DEPENDENT_FALSE_HPP
#define BOOST_TYPE_TRAITS_DEPENDENT_FALSE_HPP

#include <boost/type_traits/integral_constant.hpp>



namespace boost
{
template <typename... Types> struct dependent_false : public false_type{};


#if !defined(BOOST_NO_CXX17_INLINE_VARIABLES)
template <typename... Types> inline constexpr bool dependent_false_v = dependent_false<Types...>::value;
#endif
}	//	boost

#endif	//	BOOST_TYPE_TRAITS_DEPENDENT_FALSE_HPP

[jzmaddock]

Use case?

[gpeterhoff]

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2593r0.html

cplusplus/papers#572