🔧 [mph] concepts::invocable

Author: kris-jusiak

README.md

@@ -187,8 +187,8 @@ template<info meta> using type_of = /* unspecified */;
  *               typeid(apply<variant>([] { return vector{meta<int>}; })));
  * @endcode
  */
-template<template<class...> class T, class Expr>
-[[nodiscard]] constexpr auto apply(Expr expr);
+template<template<class...> class T>
+[[nodiscard]] constexpr auto apply(concepts::invocable auto expr);
 ```
 
 ```cpp

mp

@@ -36,6 +36,8 @@ template<size_t N> using make_index_sequence =
 namespace concepts {
 template<class TRange>
 concept range = requires(TRange range) { range.begin(); range.end(); };
+template<class Fn, class... TArgs>
+concept invocable = requires (Fn fn, TArgs... args) { fn(args...); };
 } // namespace concepts
 
 /**
@@ -166,7 +168,7 @@ using type_of = typename decltype(get(detail::meta_type<meta>{}))::value_type;
  * @endcode
  */
 template<template<class...> class T>
-[[nodiscard]] constexpr auto apply(auto expr) {
+[[nodiscard]] constexpr auto apply(concepts::invocable auto expr) {
   constexpr concepts::range auto range = expr();
   return [range]<size_t... Ns>(utility::index_sequence<Ns...>) {
     return T<type_of<range[Ns]>...>{};