Re: [Boost-users] Boost preprocessor question

Subject: Re: [Boost-users] Boost preprocessor question
From: Michiel Helvensteijn (m.helvensteijn_at_[hidden])
Date: 2009-01-05 18:11:05

Pete Bartlett wrote:

>>What about:
>>
>>CLASS(Foo, FROM(Bar),
>>    CONSTRUCT(BOOST_PP_EMPTY_SEQ)
>>    CONSTRUCT((int, a, A)(bool, b, B))
>>    int A;
>>    bool B;
>>)
> 
>>Might that not be a way to avoid the Foo repetition?
> 
> It would have to look like
> 
> CLASS( Foo, FROM(Bar)
> , CONSTRUCT(  BOOST_PP_EMPTY_SEQ )
>   CONSTRUCT( (int, a, A)(bool, b, B) )
> , int A ; bool B ;
> )
> 
> where you have
> 
> #define CONSTRUCT(sequence) sequence

Why wouldn't my example work?

> and the CLASS macro does all the work. The macro implementation would be
> slightly more complicated because of the nested FOR_EACHs (degrading
> maintainability) and debuggability will be impaired, but perhaps still
> better than introducing an external code generator to your build setup.

You know, I just realized it's not possible after all, since I will also add
enums and structs as sub-types sometimes. They contain comma's, which would
break the macro-call. I'll use the END_CLASS notation and accept the Foo
repetition. :-)

> Nb it seems like the 'a' and 'b' are superfluous - the constructor
> parameters could be written something like BOOST_PP_CAT(membervarname , _
> ).

Good point! How could I have missed that one?

Thanks!

-- 
Michiel Helvensteijn