set visual studio flags to accurately report and use latest c++ features.

CMakeLists.txt

@@ -125,7 +125,7 @@ if (PHMAP_BUILD_EXAMPLES)
     if(NOT MSVC)
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic -Wall -Wextra -Wcast-align -Wcast-qual -Wdisabled-optimization -Winit-self -Wlogical-op -Wmissing-include-dirs -Woverloaded-virtual -Wredundant-decls -Wshadow -Wstrict-null-sentinel  -Wswitch-default -Wno-unused -Wno-unknown-warning-option -Wno-gnu-zero-variadic-macro-arguments")
     else()
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4 /Zc:__cplusplus /std:c++latest")
     endif()
 
     set(THREADS_PREFER_PTHREAD_FLAG ON)

cmake/helpers.cmake

@@ -26,7 +26,7 @@ function(phmap_cc_test)
   )
 if(MSVC)
   target_compile_options(${_NAME}
-    PRIVATE ${PHMAP_CC_TEST_CWOPTS} /W4
+    PRIVATE ${PHMAP_CC_TEST_CWOPTS} /W4 /Zc:__cplusplus /std:c++latest
   )
 else()
   target_compile_options(${_NAME}