Re: [boost] Alternative implementation for BOOST_PP_VARIADIC_SIZE

Subject: Re: [boost] Alternative implementation for BOOST_PP_VARIADIC_SIZE
From: Jens Gustedt (jens.gustedt_at_[hidden])
Date: 2011-11-15 05:22:51

Paul Mensonides <pmenso57 <at> comcast.net> writes:

> On Mon, 14 Nov 2011 19:13:17 +0000, Jens Gustedt wrote:
> (Excluding the pathological case of a unbalanced parenthesis.)

Paul
thanks a lot for your detailed explanation.

yes, I am not interested in that case. I don't expect a
compiler/preprocessor to don anything sensible when someone tries to
pass in expressions that lead to unbalanced parenthesis.

> You can make it work with input terminating in a function-like macro at
> the cost of making it not work for other things.

Still (even with your explanations below) I don't capture cases that
my macro wouldn't handle.

> The other way is by intentionally putting a (variadic) function-like macro
> name in front of the argument and a () after the argument which may expand
> against the argument and may expand against the trailing () that you
> added.  However, if the argument ends in a function-like macro name, you
> have no idea what that macro is, what its arity is, what it expands to,
> etc..

my macro does a case analysis of four different scenarios and decides
upon that. And I re-read the standard (C99) several times and
implemented my own preprocessor to see if I captured all corner cases.

Maybe I overlooked a case, then it should be possible to add that or
at least it should be possible to document that behavior. So I would
be very curious if you could point me on a concrete example of such a
case.

> The bottom line is that there is no general way to interact with the
> argument that doesn't cause compiler errors with some input.

Please, be more concrete and show me such an input.

Jens