Is it possible to implement always_false in the C++ standard library?

Question

There are cases where one uses an always_false helper to e.g. cause unconditional static_assert failure if instantiation of some template is attempted:

Answer 1

In C++20, with lambda, you might do something like:

template  struct always_false : std::false_type {};

// To have true, but for a type that user code can't reuse as lambda types are unique.
template <> struct always_false : std::true_type{};