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

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2003-04-29 05:56:36

Paul Mensonides wrote:
> 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.

Thank you! The fix is greatly appreciated.

> 
> 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.

Oh well. Thanks anyway!

Aleksey