Bugfix/issue 20 allow non copyable non movable return types

.appveyor.yml

@@ -1,11 +1,21 @@
 os:
-- Visual Studio 2015
-- Visual Studio 2017
+  - Visual Studio 2017
+  - Visual Studio 2015
+
+environment:
+  matrix:
+    - STD: 17
+    - STD: 14
 
 build_script:
   - git submodule update --init --recursive
   - mkdir build
   - cd build
-  - cmake ..
+  - cmake -DCMAKE_CXX_STANDARD=%STD% -DCMAKE_CXX_STANDARD_REQUIRED=True ..
   - cmake --build .
   - C:\projects\function-ref\build\Debug\tests.exe
+
+matrix:
+  exclude:
+    - os: Visual Studio 2015
+      STD: 17

.travis.yml

@@ -5,6 +5,14 @@ sudo: false
 
 matrix:
   include:
+    - compiler: gcc
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-7
+      env: COMPILER=g++-7 CXX_STANDARD=17
     - compiler: gcc
       addons:
         apt:

CMakeLists.txt

@@ -1,40 +1,50 @@
-cmake_minimum_required(VERSION 3.11)
-
-project(tl-function_ref VERSION 1.0.0 LANGUAGES CXX)
-
-option(FUNCTION_REF_ENABLE_TESTS "Enable tests." ON)
-
-include(FetchContent)
+cmake_minimum_required(VERSION 3.11)
+
+project(tl-function_ref VERSION 1.0.0 LANGUAGES CXX)
+
+option(FUNCTION_REF_ENABLE_TESTS "Enable tests." ON)
+
+include(FetchContent)
 FetchContent_Declare(
   tl_cmake
-  GIT_REPOSITORY https://github.com/TartanLlama/tl-cmake.git
-)
+  GIT_REPOSITORY https://github.com/burnpanck/tl-cmake.git
+  GIT_TAG b6fe9104d205cf04c4aac3824c2d310959b66120
+)
 FetchContent_GetProperties(tl_cmake)
 if(NOT tl_cmake_POPULATED)
   FetchContent_Populate(tl_cmake)
   set(CMAKE_MODULE_PATH ${tl_cmake_SOURCE_DIR} ${CMAKE_MODULE_PATH})
-endif()
-include(add-tl)
-
-tl_add_library(function-ref SOURCES 
-               include/tl/function_ref.hpp)
-
-# Prepare "Catch" library for other executables
-set(CATCH_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/test)
-add_library(Catch INTERFACE)
-target_include_directories(Catch INTERFACE ${CATCH_INCLUDE_DIR})
-
-if(FUNCTION_REF_ENABLE_TESTS)
-  # Make test executable
-  set(TEST_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/tests/main.cpp
-    ${CMAKE_CURRENT_SOURCE_DIR}/tests/constructors.cpp
-    ${CMAKE_CURRENT_SOURCE_DIR}/tests/call.cpp  
-    ${CMAKE_CURRENT_SOURCE_DIR}/tests/issues.cpp
-    ${CMAKE_CURRENT_SOURCE_DIR}/tests/assignment.cpp)
-
-  add_executable(tests ${TEST_SOURCES})
-
-  target_link_libraries(tests Catch function-ref)
-
-  set_property(TARGET tests PROPERTY CXX_STANDARD 14)
-endif()
+endif()
+include(add-tl)
+
+tl_add_library(function-ref ARCH_INDEPENDENT SOURCES 
+               include/tl/function_ref.hpp)
+
+# make sure we see the C++ version, even in MSVC:
+# https://stackoverflow.com/questions/57102212/cannot-set-cplusplus-to-c17-standard-with-visual-studio-and-cmake
+if ((MSVC) AND (MSVC_VERSION GREATER_EQUAL 1914))
+  target_compile_options(function-ref INTERFACE "/Zc:__cplusplus")
+endif()
+
+# Prepare "Catch" library for other executables
+set(CATCH_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/test)
+add_library(Catch INTERFACE)
+target_include_directories(Catch INTERFACE ${CATCH_INCLUDE_DIR})
+
+if(FUNCTION_REF_ENABLE_TESTS)
+  # Make test executable
+  set(TEST_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/tests/main.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/tests/constructors.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/tests/call.cpp  
+    ${CMAKE_CURRENT_SOURCE_DIR}/tests/issues.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/tests/assignment.cpp)
+
+  add_executable(tests ${TEST_SOURCES})
+
+  target_link_libraries(tests Catch function-ref)
+
+  message(STATUS "CMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD}")
+  if(NOT CMAKE_CXX_STANDARD)
+    set_property(TARGET tests PROPERTY CXX_STANDARD 14)
+  endif()
+endif()

include/tl/function_ref.hpp

@@ -109,12 +109,20 @@ using invoke_result = invoke_result_impl<F, void, Us...>;
 template <class F, class... Us>
 using invoke_result_t = typename invoke_result<F, Us...>::type;
 
+#if __cplusplus >= 201703
+template <typename From, typename To>
+using is_prvalue_convertible = std::bool_constant<std::is_same_v<From,To> || std::is_convertible_v<From,To>>;
+#else
+template <typename From, typename To>
+using is_prvalue_convertible = std::is_convertible<From,To>;
+#endif
+
 template <class, class R, class F, class... Args>
 struct is_invocable_r_impl : std::false_type {};
 
 template <class R, class F, class... Args>
 struct is_invocable_r_impl<
-    typename std::is_convertible<invoke_result_t<F, Args...>, R>::type, R, F, Args...>
+    typename is_prvalue_convertible<invoke_result_t<F, Args...>, R>::type, R, F, Args...>
     : std::true_type {};
 
 template <class R, class F, class... Args>

tests/issues.cpp

@@ -29,4 +29,20 @@ TEST_CASE("Issue #10") {
   int z = 12;
   auto f = [&](const std::vector<int> i) { return i[0] * z; };
   foo(f);
-}
+}
+
+#if __cplusplus >= 201703
+struct NonCopyNonMove {
+  NonCopyNonMove() = default;
+  NonCopyNonMove(const NonCopyNonMove &) = delete;
+  NonCopyNonMove(NonCopyNonMove &&) = delete;
+};
+
+TEST_CASE("Issue #20") {
+  auto f = []() { return NonCopyNonMove(); };
+  auto fr = tl::function_ref<NonCopyNonMove()>(f);
+
+  // silence warnings
+  (void)fr;
+}
+#endif