-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Daniel James
Paul Mensonides wrote:
1. Use of PP_SEQ interface to "parse" function name and arguments
int X::foo(char* buf, size_t len) { BOOST_TRACE_MEM_FUN( (foo)(buf, len) );
^^^^^^^^
You can't do this without variadic macros (ala C99). We should have these in C++ eventually, but we don't right now and the pp-lib doesn't support them.
I think he's just using BOOST_PP_SEQ_TAIL to get the arguments. This means that they're never directly accessed by the sequence macros.
SEQ_TAIL *is* a sequence macro.
For example:
#define ARGUMENT_STRING(fn) BOOST_PP_STRINGIZE(BOOST_PP_SEQ_TAIL(fn))
ARGUMENT_STRING((foo)(buf, len)) // Expands to "(buf, len)"
That works on g++, although I don't know how portable it is.
It works because of a poorly-designed gcc extension. It shouldn't. The only thing that you can do with a sequence that contains a non-unary element is process the elements before it. You cannot touch it in any way; you cannot even test whether or not it is non-unary. In the case of SEQ_TAIL, it has to go through the non-unary element to tell where the end is which should result in the wrong number of arguments (2) to a macro (which takes 1). Even with variadics, it should *still* be an error because the library isn't currently designed to handle it. (I.e. there is not a single instance of ... in any parameter list of any macro in the entire library.) Regards, Paul Mensonides