Better Enums

Extending limits

The BETTER_ENUM macro makes heavy use of the preprocessor, and some of the internal macros have size limits. There are two: on the number of constants you can declare, and on the maximum length of a constant name under very specific conditions. If you run into either one, you can extend the limit by following the instructions on this page.

The second limit, on the maximum length of a constant name, applies only when you are compiling an enum in "full" constexpr mode and the constant has an initializer. Otherwise, your constants can have names of arbitrary length.

The default limits are 64 constants in an enum and 23 characters for initialized constants of full-constexpr enums. To extend:

1. Pick your desired limits. I will use 512 constants and 63 characters as an example. Add 1 to the number of characters to account for the null terminator — our numbers are now 512 and 64.
2. Get make_macros.py from your copy of the full Better Enums distribution or from GitHub.
3. You will run this script to generate a header file containing some replacement macros for enum.h to use. Pick a name for this file and a location somewhere in your include path. I will assume that this file is common/enum_macros.h in your project.
4. Run python make_macros.py 512 64 > common/enum_macros.h.

5. Define BETTER_ENUMS_MACRO_FILE <common/enum_macros.h> before including enum.h. This is typically done by supplying extra flags to the compiler on the command line:

   • For g++ and clang++, -DBETTER_ENUMS_MACRO_FILE='<common/enum_macros.h>'
   • For VC++, \DBETTER_ENUMS_MACRO_FILE='<common/enum_macros.h>'
   • With CMake, you may need something like add_definitions(-DBETTER_ENUMS_MACRO_FILE="${CMAKE_SOURCE_DIR}/src/enum-macros.h")

   You can also create a new header file that defines this macro, and then includes enum.h. Then, include your new file everywhere where you would otherwise include enum.h:

   #pragma once
   
   #define BETTER_ENUMS_MACRO_FILE <common/enum_macros.h>
   #include <enum.h>

6. Enjoy the looser limits. Just watch out — increasing the second number can really slow down compilation of full-constexpr enums.

7. You don't need make_macros.py anymore. It's not part of your build process and you can delete it.

I am paying attention to feedback, so if more than a few users say that the default limit of 64 constants is too low, I will increase it to simplify everyone's command line. The current choice of 64 is basically an arbitrary guess, loosely informed by the following two facts about macro parameter limits:

• The default limit in Boost.Preprocessor is 64. Though Better Enums does not use Boost, I took this number as a guideline.
• The next power of two, 128, is more than the number Visual C++ supports (127).