gistfile1.txt

template <typename T>
using Invoke = typename T::type;

// identity meta-function
template <typename T>
struct id { using type = T; };

// `int` meta-constant
template <int I>
using Int = std::integral_constant<int, I>;

// `bool` meta-constant
template <bool B>
using Bool = std::integral_constant<bool, B>;
using True = Bool<true>;
using False = Bool<false>;

// if-then-else meta-function
template <typename Condition, typename Then, typename Else>
using Conditional = Invoke<std::conditional<Condition::value, Then, Else>>;

// Boolean negation meta-function
template <typename T>
using Not = Bool<!T::value>;
//
// Boolean disjunction meta-function
template <typename... T>
struct any : False {};
template <typename Head, typename... Tail>
struct any<Head, Tail...> : Conditional<Head, True, any<Tail...>> {};
template <typename... T>
using Any = Invoke<any<T...>>;

// Boolean conjunction meta-function
template <typename... T>
struct all : True {};
template <typename Head, typename... Tail>
struct all<Head, Tail...> : Conditional<Head, all<Tail...>, False> {};
template <typename... T>
using All = Invoke<all<T...>>;

// Conditional overload enabler
template <typename... T>
using EnableIf = Invoke<std::enable_if<All<T...>::value, int>>;

// Conditional overload disabler
template <typename... T>
using DisableIf = Invoke<std::enable_if<!Any<T...>::value, int>>;