Overloading Macro on Number of Arguments

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Simple as:

#define GET_MACRO(_1,_2,_3,NAME,...) NAME
#define FOO(...) GET_MACRO(__VA_ARGS__, FOO3, FOO2)(__VA_ARGS__)

So if you have these macros, they expand as described:

FOO(World, !)         // expands to FOO2(World, !)
FOO(foo,bar,baz)      // expands to FOO3(foo,bar,baz)

If you want a fourth one:

#define GET_MACRO(_1,_2,_3,_4,NAME,...) NAME
#define FOO(...) GET_MACRO(__VA_ARGS__, FOO4, FOO3, FOO2)(__VA_ARGS__)

FOO(a,b,c,d)          // expands to FOO4(a,b,c,d)

Naturally, if you define FOO2, FOO3 and FOO4, the output will be replaced by those of the defined macros.

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