What does the #define ROBJECT_EMBED_LEN_MAX ROBJECT_EMBED_LEN_MAX do?

Question

Browsing through MRI's code, I found these #defines I don't understand:

#define ROBJECT_EMBED_LEN_MAX ROBJECT_EMBED_LEN_MAX
#define ROBJECT_EMBED ROBJECT_EMBED
enum {
    ROBJECT_EMBED_LEN_MAX = 3,
    ROBJECT_EMBED = RUBY_FL_USER1,

    ROBJECT_ENUM_END
};

What's the point of those #defines? They seem to do nothing...

This code is found in the ruby/include/ruby/ruby.h file in the ruby github repo.

@AlexanderO'Mara No, it's not, this define seems to be referencing the enum. — csTroubled, Aug 24 '16 at 02:34
It's not a multi-line macro: http://stackoverflow.com/questions/16685211/c-define-multiline-macro — Alexander O'Mara, Aug 24 '16 at 02:36
Possible duplicate of [Redefining enum enumerators with #define](http://stackoverflow.com/questions/6830602/redefining-enum-enumerators-with-define) — Jason C, Aug 24 '16 at 03:38

score 0 · Answer 1 · answered Aug 24 '16 at 02:34

The #defines make it possible to test for the existence of the definition at compile-time using #ifdef. (You cannot test for the existence of an enum at compile-time.)

Since the C preprocessor doesn't do recursive substitution, defining a symbol as itself effectively does nothing; the symbol is replaced once with itself, and then passed normally to the compiler.

What does the #define ROBJECT_EMBED_LEN_MAX ROBJECT_EMBED_LEN_MAX do?

1 Answers1