Compiler version specific configuration support added

src/CMakeLists.txt

@@ -29,10 +29,13 @@ project(units
 )
 
 # set path to custom cmake modules
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/../cmake/common/cmake")
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # include common tools and workarounds
-include(tools)
+include(common/cmake/tools)
+
+# check availability of C++20 features
+include(check_features)
 
 # library definition
 add_library(units INTERFACE)
@@ -59,7 +62,7 @@ target_link_libraries(units
 target_include_directories(units
     INTERFACE
         $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/include>
         $<INSTALL_INTERFACE:include>
 )
 add_library(mp::units ALIAS units)
@@ -75,6 +78,10 @@ install(DIRECTORY include/units
     DESTINATION include
     COMPONENT Devel
 )
+install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/include/units
+    DESTINATION include
+    COMPONENT Devel
+)
 
 # generate configuration files and install the package
 configure_and_install(../cmake/common/cmake/simple_package-config.cmake.in mp SameMajorVersion)

src/include/units/bits/hacks.h

@@ -22,10 +22,13 @@
 
 #pragma once
 
+#include <units/bits/config.h>
 #include <experimental/ranges/concepts>
 
 namespace std {
 
+#ifndef UNITS_HAS_STD_TYPE_IDENTITY
+
   // type_identity
   template<typename T>
   struct type_identity { using type = T; };
@@ -33,6 +36,8 @@ namespace std {
   template<typename T>
   using type_identity_t = typename type_identity<T>::type;
 
+#endif // UNITS_HAS_STD_TYPE_IDENTITY
+
   // concepts
   using experimental::ranges::Same;
   using experimental::ranges::Integral;