Add potswa/cxx_function@e7beb8bfe as second test type erasure backend

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "dep/function2/function2"]
 	path = dep/function2/function2
 	url = https://github.com/Naios/function2.git
+[submodule "dep/cxx_function/cxx_function"]
+	path = dep/cxx_function/cxx_function
+	url = https://github.com/potswa/cxx_function.git

dep/CMakeLists.txt

@@ -2,6 +2,10 @@ if(CONTINUABLE_UNIT_TESTS AND NOT TARGET gtest)
   add_subdirectory(googletest)
 endif()
 
+if(CONTINUABLE_UNIT_TESTS AND NOT TARGET cxx_function)
+  add_subdirectory(cxx_function)
+endif()
+
 if(NOT TARGET function2)
   add_subdirectory(function2)
 endif()

dep/cxx_function/CMakeLists.txt

@@ -0,0 +1,5 @@
+add_library(cxx_function INTERFACE)
+
+target_include_directories(cxx_function
+  INTERFACE
+    "${CMAKE_CURRENT_LIST_DIR}")

dep/cxx_function/cxx_function

@@ -0,0 +1 @@
+Subproject commit 8220501d0db1bcdd28a11c958f623c079c243000

test/unit-test/CMakeLists.txt

@@ -14,6 +14,7 @@ foreach(STEP RANGE 4)
   target_link_libraries(${PROJECT_NAME}
     PRIVATE
       gtest-main
+      cxx_function
       continuable)
 
   target_compile_definitions(${PROJECT_NAME}

test/unit-test/test-continuable.hpp

@@ -29,8 +29,18 @@
 #include "continuable/continuable-base.hpp"
 #include "continuable/continuable-testing.hpp"
 #include "continuable/continuable.hpp"
+#include "cxx_function/cxx_function.hpp"
 #include "gtest/gtest.h"
 
+template <typename... Args>
+using cxx_trait_of = cti::continuable_trait<cxx_function::function,
+                                            cxx_function::function, Args...>;
+
+template <typename... Args>
+using unique_cxx_trait_of =
+    cti::continuable_trait<cxx_function::unique_function,
+                           cxx_function::unique_function, Args...>;
+
 using cti::detail::util::identity;
 
 inline auto to_hint(identity<> /*hint*/) { return identity<void>{}; }