Overload C/C++ preprocessor macro on structure of its argument

Question

I would like to write a preprocessor macro that does one thing if it\'s argument is a parenthesized tuple of tokens, like this:

MY_MACRO((x, y))

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Answer 1

As for your first question, the following macros might meet your purpose:

#define CONCAT_( x, y ) x ## y
#define CONCAT( x, y ) CONCAT_( x, y )
#define IS_SINGLE_1(...) 0
#define IGNORE(...)
#define IS_SINGLE_2_0           0 IGNORE(
#define IS_SINGLE_2_IS_SINGLE_1 1 IGNORE(
#define IS_SINGLE( x ) CONCAT( IS_SINGLE_2_, IS_SINGLE_1 x ) )
IS_SINGLE((x, y)) // 0
IS_SINGLE(x)      // 1

Macro IS_SINGLE is expanded to 1 if the argument is single token, otherwise, 0.

Hope this helps