Re: [boost] Review Request: Variadic Macro Data library

Subject: Re: [boost] Review Request: Variadic Macro Data library
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2011-02-21 15:24:12

> >> * Note that I don't know of a single preprocessor that actually
> >> handles whitespace correctly in all cases.
> >
> > Damn, I know I had that right in Wave at some point. Must have broken
> > it later... And apparently there are no tests in Wave verifying this
> > is functioning as expected.
> >
> > I'll fix both things asap.
> 
> Note that there is only one way that the lack of proper handling can
> effect the semantics of a program: stringizing.  Further, it must internal
> whitespace because stringizing removes leading and trailing whitespace and
> condenses adjacent internal whitespace by definition-- which you can get
> because the normal whitespace condensation happens in an earlier separate
> phase:
> 
> #define A(x) 1 x 3
> 
> A(2)   // 1 2 3
> A( 2 ) // 1  2  3

This is the only place in Wave I found so far where the whitespace is not
preserved, I get 

   A( 2 ) // 1 2 3

I'll see what I can do, though.

> When stringized these both result in "1 2 3".  However, something like
> this is where things change:
> 
> #define B(x) (1)x(3)
> 
> STRINGIZE(B(3))   // "(1)3(2)"
> STRINGIZE(B( 3 )) // "(1) 3 (2)" -- aha! different semantics

Well, that depends on how you define the STRINGIZE() macro. It might not
expand the B() at all :-P

In any case, this is handled properly in Wave. 

> Other than scenarios like that, it makes no effective difference.

Sure.

Regards Hartmut
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