[boost] Re: Empty sequence elements

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2005-03-03 14:06:25

Paul Mensonides wrote:
>>-----Original Message-----
>>From: boost-bounces_at_[hidden] 
>>[mailto:boost-bounces_at_[hidden]] On Behalf Of Tobias Schwinger
> 
> 
>>Thank you for this very detailed reply !
>>
>>Is it safe to use BOOST_PP_EMTPY or 
>>BOOST_PP_INDENTITY(somthing) as the element and "dereference" 
>>with '()' ?
> 
> 
> Sure, provided that the result is never "bound" to an argument by itself.  E.g.
> 
> #define A(x) B(x)
> #define B(x) x
> 
> A() // undefined: empty argument to A
> 
> A( BOOST_PP_EMPTY() ) // undefined: empty argument to B
> 
> A( BOOST_PP_EMPTY )() // okay
^^^

This is about what I meant (well, BOOST_PP_SEQ_ELEM(x,s)() - x being the 
index of the "optional element" in a sequence). But according to the 
source of SEQ_ELEM this should work as well.

Thanx, again.

Regards,

Tobias