From ff0a5f9f4a4040c6f992581245fed48d9634acfe Mon Sep 17 00:00:00 2001
From: Robert Ramey <ramey@rrsd.com>
Date: Thu, 2 Nov 2023 20:17:08 -0700
Subject: [PATCH] corrected inclusion of <optional>

---
 CMake/CMakeLists.txt                     | 11 ++++++-----
 include/boost/serialization/optional.hpp |  2 +-
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/CMake/CMakeLists.txt b/CMake/CMakeLists.txt
index ddacdbd5b..9904b66aa 100644
--- a/CMake/CMakeLists.txt
+++ b/CMake/CMakeLists.txt
@@ -21,7 +21,6 @@ add_definitions(${Boost_LIB_DIAGNOSTIC_DEFINITIONS})
 message(STATUS "C compiler is ${CMAKE_C_COMPILER_ID}" )
 
 if( CMAKE_CXX_COMPILER_ID STREQUAL "GNU" )
-  add_definitions( -std=c++11 )
   add_definitions( -ftemplate-depth=255 )
   # we use gcc to test for C++03 compatibility
   set(COMPILER_SUPPORTS_CXX11 FALSE)
@@ -29,17 +28,19 @@ elseif( CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" )
   add_definitions( /wd4996 )
   set(COMPILER_SUPPORTS_CXX11 TRUE)
 elseif( CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" )
-  add_definitions( -std=c++17 )
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -ftemplate-depth=300")
-  #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++03")
-  #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")
   set(CMAKE_CXX_FLAGS_DEBUG "-g -O0" )
   set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-g -O3" )
   set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -stdlib=libc++ -dead_strip")
   set(COMPILER_SUPPORTS_CXX11 TRUE)
 endif()
 
+add_definitions( -std=c++20 )
+#set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++03")
+#set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+#set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++20")
+
 #
 # Locate Project Prerequisites 
 #
diff --git a/include/boost/serialization/optional.hpp b/include/boost/serialization/optional.hpp
index c736eabfa..668f99406 100644
--- a/include/boost/serialization/optional.hpp
+++ b/include/boost/serialization/optional.hpp
@@ -16,7 +16,7 @@
 
 #include <boost/config.hpp>
 #include <boost/optional.hpp>
-#ifdef BOOST_NO_CXX17_HDR_OPTIONAL
+#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
 #include <optional>
 #endif