Re: [boost] PP: MSVC BOOST_PP_REPEAT + BOOST_PP_SEQ_ELEM bug

From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2003-04-18 01:40:23

Aleksey Gurtovoy wrote:
> Paul Mensonides wrote:
>>> Yep, they do - that's why I named it "BOOST_PP_REPEAT +
>>> BOOST_PP_SEQ_ELEM bug".
>>
>> That is what I figured, but I wanted to make sure that the (a, b, c)
>> wasn't causing a problem--which it shouldn't be anyway.  I'll look
>> at this later when I have time to install VC6 on my other computer.
>
> That would be much appreciated.

Okay, this is "fixed," but before you update, this is the reduction of the
problem.  First, it has nothing to do with BOOST_PP_REPEAT per se.  Rather it is
the kind of instability that I mentioned before relative to IS_UNARY, since
SEQ_ELEM does a similar kind of thing.  Take a look:

#include <boost/preprocessor/seq/elem.hpp>

#define X() ...

#define A(seq) BOOST_PP_SEQ_ELEM(0, seq)
#define B(seq) (BOOST_PP_SEQ_ELEM(0, seq))
#define C(seq) ID( BOOST_PP_SEQ_ELEM(0, seq) )
#define D(seq) ID(( BOOST_PP_SEQ_ELEM(0, seq) ))

#define ID(x) x

A( (X)(Y) ) //  X
B( (X)(Y) ) // (X)
C( (X)(Y) ) //  X
D( (X)(Y) ) //  0

The last one is wrong.  It should expand to (X).  This should be fixed now, but
it illustrates the kind of encapsulation issues that I was referring to before.

As far as the other bug is concerned, here is the reduction of the problem:

// entire file...
#define M()

M

VC6 expects to find the open parentheses of a macro invocation, but instead it
finds EOF.  There is nothing that I can do to fix this one.  However, VC7 seems
to have fixed this problem, at least.

Regards,
Paul Mensonides