How to make a variadic is_same?

Question

How can I make a class template that returns whether any of its variadic types are equal to the first type. I want to be able to do this:

is_same

        

Answer 1

Nice and concise with C++17:

template 
struct is_any : std::disjunction...> {};

And the dual:

template 
struct are_same : std::conjunction...> {};

A variation that uses fold expressions:

template 
struct is_any : std::bool_constant<(std::is_same_v || ...)> {};

template 
struct are_same : std::bool_constant<(std::is_same_v && ...)> {};