Make c++ version check be in the header instead of cmake.

Author: JeffGarland

CMakeLists.txt

@@ -4,17 +4,6 @@ cmake_minimum_required(VERSION 3.25)
 
 project(beman.scope DESCRIPTION "Generic Scope Guard" LANGUAGES CXX)
 
-# Define an option for the C++ standard with a default of 20
-# tbd remove: option(CXX_STANDARD "C++ standard to use (minimum C++20)" 20)
-
-# Ensure the specified standard is at least C++20
-if(CMAKE_CXX_STANDARD LESS 20)
-    message(FATAL_ERROR "The minimum required C++ standard is C++20")
-endif()
-
-# Set the C++ standard based on the user input
-# tbd remove:set(CMAKE_CXX_STANDARD ${CXX_STANDARD})
-
 enable_testing()
 
 # [CMAKE.SKIP_TESTS]

include/beman/scope/scope.hpp

@@ -6,6 +6,10 @@
 #include <type_traits>
 #include <utility>
 
+#if __cplusplus < 202002L
+  #error "C++20 or later is required"
+#endif
+
 #include <experimental/scope>
 
 namespace beman::scope {