Empty argument list

[Jiboo]

#define TRANSFORM_DECLTYPE(MInput) decltype(MInput)
#define DECLTYPE_LIST(...) MAP_LIST(TRANSFORM_DECLTYPE, __VA_ARGS__)
DECLTYPE_LIST(a,b,c)
DECLTYPE_LIST()

Results in:

decltype(a), decltype(b), decltype(c)
decltype()

I expected the case where no arguments are passed to expand to nothing, note that MAP has the same behaviour.
I fixed for my case by changing definition of TRANSFORM_DECLTYPE to #define TRANSFORM_DECLTYPE(...) __VA_OPT__(decltype(__VA_ARGS__)) but that would only work for C++2a compilers.

[namniav]

In the above example, MAP_LIST(TRANSFORM_DECLTYPE, __VA_ARGS__) is expanded to MAP_LIST(TRANSFORM_DECLTYPE, ) which has a semicolon and an "empty" argument after it. The semicolon can be avoided using ##__VA_ARGS__. However it doesn't fix the issue.
A shorter example:

#define FOO(A) foo
MAP(FOO)

is expaneded to foo.

[swansontec]

Indeed, this seems like the wrong behavior. I don't have much free time to work on this, but I'll prioritize reviewing any PR's that might fix it.