std::experimental::conjunction(3)

NAME
std::experimental::conjunction - std::experimental::conjunction

Synopsis
   Defined in header <experimental/type_traits>
   template< class... B > (library fundamentals TS v2)
   struct conjunction;
   Forms the logical conjunction of the type traits B..., effectively performing a
   logical AND on the sequence of traits.
   The specialization std::experimental::conjunction<B1, ..., BN> has a public and
   unambiguous base that is
     * if sizeof...(B) == 0, std::true_type; otherwise
     * the first type Bi in B1, ..., BN for which bool(Bi::value) == false, or BN if
       there is no such type.
   The member names of the base class, other than conjunction and operator=, are not
   hidden and are unambiguously available in conjunction.
   Conjunction is short-circuiting: if there is a template type argument Bi with
   bool(Bi::value) == false, then instantiating conjunction<B1, ..., BN>::value does
   not require the instantiation of Bj::value for j > i.

Template parameters
   B... - every template argument Bi for which Bi::value is instantiated must be usable
          as a base class and define member value that is convertible to bool
   Helper variable template
   template< class... B >
   constexpr bool conjunction_v = (library fundamentals TS v2)
   conjunction<B...>::value;

Possible implementation
   template<class...> struct conjunction : std::true_type {};
   template<class B1> struct conjunction<B1> : B1 {};
   template<class B1, class... Bn>
   struct conjunction<B1, Bn...>
       : std::conditional_t<bool(B1::value), conjunction<Bn...>, B1> {};

Notes
   A specialization of conjunction does not necessarily inherit from either
   std::true_type or std::false_type: it simply inherits from the first B
   whose ::value, converted to bool, is false, or from the very last B when all of them
   convert to true. For example, conjunction<std::integral_constant<int, 2>,
   std::integral_constant<int, 4>>::value is 4.

Example
// Run this code
 #include <experimental/type_traits>
 #include <iostream>
 // func is enabled if all Ts... have the same type
 template<typename T, typename... Ts>
 constexpr std::enable_if_t<std::experimental::conjunction_v<std::is_same<T, Ts>...>>
 func(T, Ts...)
 {
     std::cout << "All types are the same.\n";
 }
 template<typename T, typename... Ts>
 constexpr std::enable_if_t<!std::experimental::conjunction_v<std::is_same<T, Ts>...>>
 func(T, Ts...)
 {
     std::cout << "Types differ.\n";
 }
 int main()
 {
     func(1, 2'7, 3'1);
     func(1, 2.7, '3');
 }

Output:
 All types are the same.
 Types differ.

See also
   conjunction variadic logical AND metafunction
   (C++17) (class template)