Update the C++ version from 17 to 20.

Author: taku910

CMakeLists.txt

@@ -50,7 +50,7 @@ if(WIN32)
   set(SPM_ENABLE_SHARED OFF)
 endif()
 
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 if((CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND

third_party/darts_clone/darts.h

@@ -1457,12 +1457,12 @@ class DoubleArrayBuilder {
   void clear();
 
  private:
-  enum { BLOCK_SIZE = 256 };
-  enum { NUM_EXTRA_BLOCKS = 16 };
-  enum { NUM_EXTRAS = BLOCK_SIZE * NUM_EXTRA_BLOCKS };
+  static constexpr int BLOCK_SIZE = 256;
+  static constexpr int NUM_EXTRA_BLOCKS = 16;
+  static constexpr int NUM_EXTRAS = BLOCK_SIZE * NUM_EXTRA_BLOCKS;
 
-  enum { UPPER_MASK = 0xFF << 21 };
-  enum { LOWER_MASK = 0xFF };
+  static constexpr int  UPPER_MASK = 0xFF << 21;
+  static constexpr int  LOWER_MASK = 0xFF;
 
   typedef DoubleArrayBuilderUnit unit_type;
   typedef DoubleArrayBuilderExtraUnit extra_type;