From 155621858078889ec4f976f227742700a8144d4e Mon Sep 17 00:00:00 2001
From: Max Golovanov <maxgolov@microsoft.com>
Date: Mon, 15 Jun 2020 14:35:58 -0700
Subject: [PATCH 1/2] std::result_of removed in C++20

---
 CMakeLists.txt                                 | 5 +++++
 api/include/opentelemetry/nostd/function_ref.h | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 264d58992d..af4c3dbe30 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -20,6 +20,11 @@ include(CTest)
 
 find_package(Threads)
 
+if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+  # Options for Visual C++ compiler
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /Zc:__cplusplus")
+endif()
+
 if(WITH_PROTOBUF)
   set(protobuf_MODULE_COMPATIBLE ON)
   find_package(Protobuf CONFIG NAMES protobuf)
diff --git a/api/include/opentelemetry/nostd/function_ref.h b/api/include/opentelemetry/nostd/function_ref.h
index 33c94d00ab..de61c7040a 100644
--- a/api/include/opentelemetry/nostd/function_ref.h
+++ b/api/include/opentelemetry/nostd/function_ref.h
@@ -63,7 +63,13 @@ class function_ref<R(Args...)>
       typename std::enable_if<!std::is_same<function_ref, typename std::decay<F>::type>::value,
                               int>::type = 0,
       typename std::enable_if<
+#if (__cplusplus >= 201703L)
+          // std::result_of deprecated in C++17, removed in C++20
+          std::is_convertible<typename std::invoke_result<F, Args...>::type, R>::value,
+#else
+          // std::result_of since C++11
           std::is_convertible<typename std::result_of<F &(Args...)>::type, R>::value,
+#endif
           int>::type = 0>
   function_ref(F &&f)
   {

From d1bd7b284b5325360c2e871e0117abe79118f98e Mon Sep 17 00:00:00 2001
From: Max Golovanov <max.golovanov+github@gmail.com>
Date: Mon, 15 Jun 2020 19:44:09 -0700
Subject: [PATCH 2/2] Update CMakeLists.txt

Address code review comment to document what /Zc:__cplusplus option is doing
---
 CMakeLists.txt | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index af4c3dbe30..2e5eee69e5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,7 +21,9 @@ include(CTest)
 find_package(Threads)
 
 if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
-  # Options for Visual C++ compiler
+  # Options for Visual C++ compiler:
+  # /Zc:__cplusplus - report an updated value for recent C++ language standards.
+  # Without this option MSVC returns the value of __cplusplus="199711L"
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /Zc:__cplusplus")
 endif()