add option in CMake

Author: uyha

CMakeLists.txt

@@ -23,16 +23,17 @@ OPTION (MSGPACK_CXX14 "Using c++14 compiler" OFF)
 OPTION (MSGPACK_CXX17 "Using c++17 compiler" OFF)
 OPTION (MSGPACK_CXX20 "Using c++20 compiler" OFF)
 
-OPTION (MSGPACK_32BIT            "32bit compile"                        OFF)
-OPTION (MSGPACK_USE_BOOST        "Use Boost libraried"                  ON)
-OPTION (MSGPACK_USE_X3_PARSE     "Use Boost X3 parse"                   OFF)
-OPTION (MSGPACK_BUILD_TESTS      "Build tests"                          OFF)
-OPTION (MSGPACK_BUILD_DOCS       "Build Doxygen documentation"          ON)
-OPTION (MSGPACK_FUZZ_REGRESSION  "Enable regression testing"            OFF)
-OPTION (MSGPACK_BUILD_EXAMPLES   "Build msgpack examples"               OFF)
-OPTION (MSGPACK_GEN_COVERAGE     "Generate coverage report"             OFF)
-OPTION (MSGPACK_USE_STATIC_BOOST "Statically link with boost libraries" OFF)
-OPTION (MSGPACK_CHAR_SIGN        "Char sign to use (signed or unsigned)")
+OPTION (MSGPACK_32BIT                   "32bit compile"                        OFF)
+OPTION (MSGPACK_USE_BOOST               "Use Boost libraried"                  ON)
+OPTION (MSGPACK_USE_X3_PARSE            "Use Boost X3 parse"                   OFF)
+OPTION (MSGPACK_BUILD_TESTS             "Build tests"                          OFF)
+OPTION (MSGPACK_BUILD_DOCS              "Build Doxygen documentation"          ON)
+OPTION (MSGPACK_FUZZ_REGRESSION         "Enable regression testing"            OFF)
+OPTION (MSGPACK_BUILD_EXAMPLES          "Build msgpack examples"               OFF)
+OPTION (MSGPACK_GEN_COVERAGE            "Generate coverage report"             OFF)
+OPTION (MSGPACK_USE_STATIC_BOOST        "Statically link with boost libraries" OFF)
+OPTION (MSGPACK_CHAR_SIGN               "Char sign to use (signed or unsigned)")
+OPTION (MSGPACK_USE_STD_VARIANT_ADAPTOR "Enable the adaptor for std::variant"  OFF)
 
 SET (CMAKE_CXX_STANDARD_REQUIRED ON)
 
@@ -92,6 +93,10 @@ ELSE ()
     TARGET_COMPILE_DEFINITIONS(msgpack-cxx INTERFACE MSGPACK_DEFAULT_API_VERSION=3)
 ENDIF ()
 
+IF (MSGPACK_USE_STD_VARIANT_ADAPTOR)
+    TARGET_COMPILE_DEFINITIONS(msgpack-cxx INTERFACE MSGPACK_USE_STD_VARIANT_ADAPTOR)
+ENDIF ()
+
 IF ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
     IF (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.1)
         INCLUDE (CheckCXXSourceCompiles)