Re: Spec draft

From: Vladimir Prus (ghost_at_[hidden])
Date: 2003-06-17 09:20:14

[moving to the mailing list]

David Abrahams wrote:
> Vladimir Prus <ghost_at_[hidden]> writes:
> > David Abrahams wrote:
> >> > Yes, but there's another case:
> >> >
> >> > lib foo : a_gcc.cpp : <toolset>gcc ;
> >> > lib foo : a_msvc.cpp : <toolset>msvc ;
> >> > lib foo : a.cpp ;
> >> >
> >> > To represent this using conditional properties, you'd need
> >> >
> >> > lib foo : <toolset>gcc:a_gcc.cpp <toolset>msvc:a_msvc.cpp
> >> > <toolset>!gcc&&<toolset>!msvc:a.cpp ;
> >>
> >> Whast's wrong with:
> >>
> >> lib foo : <toolset>gcc:a_gcc.cpp <toolset>msvc:a_msvc.cpp
> >> <toolset>:a.cpp ;
> >
> > The problem is that <toolset>:a.cpp is not defined ;-) The only two
> > contexts where feature names alone are allowed are generator matching and
> > flags. In both context it means "any value of feature". I'm sure you have
> > some other semantic in this case, but you did not tell which.
>
> I mean "any value of feature"... except those values which are being
> used as a more-explicit condition, and thus overridde this condition.

"used as a more-explicit condition" --- you mean that if <toolset>gcc is used 
in condition anywhere in this target?

> >> Examples, please?
> >
> > lib foo : : <name>gcc_r <toolset>gcc <variant>debug ;
> > lib foo : : <name>gcc <toolset>gcc <variant>release
> > lib foo : : <name>msvc <toolset>msvc ;
> > lib foo : foo.cpp ;
> >
> > IMO, this will explode to:
> >
> > lib foo : :
> > <toolset>!msvc&&<toolset>!gcc||(<toolset>gcc&&<variant>!release&&<variant
> >>!debug):<source>foo.cpp <toolset>msvc:<name>msvc
> > <toolset>gcc,<variant>debug:<name>gcc
> > <toolset>gcc,<variant>release:<name>gcc_r
>
> Oh that's just too weird! Some of those requirements are used for
> matching (toolset, variant), and some get imposed (name)? I think I
> understand something Ali was complaining about now!

Somehow, I do not remember user complains about it. Moreover, this is 
*precisely* how requirements work. Non-free requirements can be used for 
matching. If you have <toolset>gcc in requirement, the target won't built 
with any other toolset. Free requirements are just added.

> Anyway, I think it explodes to something like:
>
> lib foo : :
> <toolset>gcc,<variant>debug:<name>gcc_r
> <toolset>gcc,<variant>release:<name>gcc
> <toolset>msvc,<variant>:<name>msvc
> <toolset>,<variant>:<source>foo.cpp
> ;

First off, to support this syntax you'd need the same logic which now selects 
alternative, right? Second, looking at this, I don't think it's obvious that 
only one line will be selected. 

- Volodya