Selective propagation of features

Hi there,



I think it would be very useful to be able to specify
features that
are propagated, but only to the targets that have declared
their
acceptance of (= dependency on) those features.

For example, one might want to build two versions of her
application:
ANSI and Unicode; she declares:

  feature charset : ansi unicode : symmetric propagated ;

However, she also wants to link with a library that does not
care
about "charset" (eg: a Boost library); it is
unnecessary to build
that library in two versions (= sub-directories)
(charset-ansi and
charset-unicode); thus, the feature should not be propagated
to it.



The workarounds that I have come up with so far are
unsatisfactory;
they do not scale well when multiple features/projects are
involved;
for example:

  feature charset : neutral ansi unicode : propagated ;
  ...
  exe Main : Main.cpp /boost//regex/<charset>neutral



I think a better solution might look like this:

  feature charset : ansi unicode :
propagated-only-to-supportive-targets ;
  ...
  lib Lib1 : Alfa.cpp :
<supports-propagation-of>charset ;
  lib Lib2 : Beta.cpp ;
  exe Main : Main.cpp Lib1 Lib2 : <charset>unicode ;



Can this be implemented (if so, how) ? Or do you know a
better
work-around ?



Thank you for your time.



-- 
Best regards,
 Adder

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on Sun Sep 23 2007, Adder <adder.thief-AT-gmail.com>
wrote:

> Hi there,
>
>
>
> I think it would be very useful to be able to specify
features that
> are propagated, but only to the targets that have
declared their
> acceptance of (= dependency on) those features.

In BBv1 we had a notion of feature relevance that did
something like
what you want, but I don't think it was carried over to BBv2
:(

-- 
Dave Abrahams
Boost Consulting
http://www.boost-cons
ulting.com

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On Wednesday 03 October 2007 06:35:09 David Abrahams wrote:
> 
> on Sun Sep 23 2007, Adder
<adder.thief-AT-gmail.com> wrote:
> 
> > Hi there,
> >
> >
> >
> > I think it would be very useful to be able to
specify features that
> > are propagated, but only to the targets that have
declared their
> > acceptance of (= dependency on) those features.
> 
> In BBv1 we had a notion of feature relevance that did
something like
> what you want, but I don't think it was carried over to
BBv2 :(

Planned for M13, FWIW. 

- Volodya
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