Concepts-related hacks added to import them to std namespace

src/include/units/bits/concepts.h

@@ -22,13 +22,13 @@
 
 #pragma once
 
-#include <experimental/ranges/concepts>
+#include <units/bits/hacks.h>
 
 namespace units {
 
   template<typename T>
-  concept bool Number = std::experimental::ranges::Regular<T> &&
-      std::experimental::ranges::StrictTotallyOrdered<T> &&
+  concept bool Number = std::Regular<T> &&
+      std::StrictTotallyOrdered<T> &&
       requires(T a, T b) {
         { a + b } -> T;
         { a - b } -> T;

src/include/units/bits/hacks.h

@@ -22,12 +22,23 @@
 
 #pragma once
 
+#include <experimental/ranges/concepts>
+
 namespace std {
 
+  // type_identity
   template<typename T>
   struct type_identity { using type = T; };
 
   template<typename T>
   using type_identity_t = typename type_identity<T>::type;
 
-}
+  // concepts
+  using experimental::ranges::Same;
+  using experimental::ranges::Integral;
+  using experimental::ranges::DerivedFrom;
+  using experimental::ranges::Regular;
+  using experimental::ranges::StrictTotallyOrdered;
+  using experimental::ranges::ConvertibleTo;
+
+}

src/include/units/bits/upcasting.h

@@ -23,7 +23,7 @@
 #pragma once
 
 #include <units/bits/hacks.h>
-#include <experimental/ranges/concepts>
+#include <type_traits>
 
 namespace units {
 
@@ -37,7 +37,7 @@ namespace units {
       requires {
         typename T::base_type;
       } &&
-      std::experimental::ranges::DerivedFrom<T, upcast_base<typename T::base_type>>;
+      std::DerivedFrom<T, upcast_base<typename T::base_type>>;
 
   template<Upcastable T>
   using upcast_from = typename T::base_type;