build: libc++ support added

src/CMakeLists.txt

@@ -30,8 +30,21 @@ project(mp-units
 set(UNITS_DOWNCAST_MODE ON CACHE STRING "Select downcasting mode")
 set_property(CACHE UNITS_DOWNCAST_MODE PROPERTY STRINGS AUTO ON OFF)
 
-# set path to custom cmake modules
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
+# check if libc++ is being used
+if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    message(CHECK_START "Checking if libc++ is being used")
+    list(APPEND CMAKE_MESSAGE_INDENT "  ")
+
+    include(CheckSymbolExists)
+    check_symbol_exists(_LIBCPP_VERSION "ciso646" UNITS_LIBCXX)
+
+    list(POP_BACK CMAKE_MESSAGE_INDENT)
+    if(UNITS_LIBCXX)
+        message(CHECK_PASS "found")
+    else()
+        message(CHECK_FAIL "not found")
+    endif()
+endif()
 
 find_package(fmt CONFIG REQUIRED)
 find_package(gsl-lite CONFIG REQUIRED)
@@ -51,11 +64,13 @@ target_include_directories(mp-units
 )
 
 if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
-    find_package(range-v3)
-    target_link_libraries(mp-units
-        INTERFACE
-            range-v3::range-v3
-    )
+    if(UNITS_LIBCXX)
+        find_package(range-v3)
+        target_link_libraries(mp-units
+            INTERFACE
+                range-v3::range-v3
+        )
+    endif()
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
     target_compile_options(mp-units
         INTERFACE

src/include/units/bits/external/hacks.h

@@ -31,15 +31,24 @@
 #define COMP_MSVC _MSC_VER
 #endif
 
-#if defined(COMP_CLANG) && !defined(UNITS_LIBCXX)
-#define UNITS_LIBCXX 0
+#if COMP_CLANG
+
+#include <ciso646>
+#if _LIBCPP_VERSION
+#define UNITS_LIBCXX _LIBCPP_VERSION
 #endif
 
-#if COMP_CLANG && UNITS_LIBCXX
+#endif
+
+#if COMP_CLANG == 12 && UNITS_LIBCXX
 
 #include <concepts/compare.hpp>
 #include <concepts/concepts.hpp>
 #include <range/v3/functional/comparisons.hpp>
+#include <range/v3/iterator.hpp>
+#include <range/v3/range/concepts.hpp>
+#include <range/v3/algorithm/lower_bound.hpp>
+#include <range/v3/algorithm/transform.hpp>
 
 #endif
 
@@ -67,35 +76,46 @@ concept default_constructible = constructible_from<T>;
 #elif COMP_CLANG && UNITS_LIBCXX
 
 // concepts
-using concepts::three_way_comparable;
-using concepts::three_way_comparable_with;
-// using concepts::common_reference_with;
 using concepts::common_with;
 using concepts::constructible_from;
 using concepts::convertible_to;
-// using concepts::default_constructible;
+using concepts::copy_constructible;
 using concepts::derived_from;
-// using concepts::equality_comparable;
+using concepts::equality_comparable;
 using concepts::equality_comparable_with;
-// // using concepts::floating_point;
-// using concepts::integral;
+using concepts::integral;
+using concepts::move_constructible;
 using concepts::regular;
-// using concepts::same_as;
-// using concepts::totally_ordered;
-// using concepts::totally_ordered_with;
+using concepts::three_way_comparable;
+using concepts::three_way_comparable_with;
+using concepts::totally_ordered;
 
 using ranges::compare_three_way;
 
-// namespace ranges {
+namespace ranges {
 
-// using ::ranges::forward_range;
-// using ::ranges::range_value_t;
+using ::ranges::begin;
+using ::ranges::end;
+using ::ranges::distance;
 
-// }
+using ::ranges::forward_range;
+using ::ranges::input_range;
+using ::ranges::range_value_t;
 
-// // missing in Range-v3
-// template<class T>
-// concept floating_point = std::is_floating_point_v<T>;
+using ::ranges::lower_bound;
+using ::ranges::transform;
+
+}
+
+// missing in Range-v3
+template<class T>
+concept floating_point = std::is_floating_point_v<T>;
+
+template<class T>
+concept default_initializable =
+    std::constructible_from<T> &&
+    requires { T{}; } &&
+    requires { ::new (static_cast<void*>(nullptr)) T; };
 
 template<class F, class... Args>
 concept invocable =