Re: [Boost-build] <asynch-exceptions>on cannot be specified inusage-requirements

From: Vladimir Prus (ghost_at_[hidden])
Date: 2006-12-18 07:31:45

On Sunday 17 December 2006 12:41, Gennadiy Rozental wrote:

> >> > error: usage-requirements <toolset>msvc:<asynch-exceptions>on have
> >> > non-free properties <asynch-exceptions>on
> >>
> >> That is rather baffling.  I can't see why usage-requirements should be
> >> limited to free properties.
> >
> > Because if you allow non-free usage requirements, then in:
> >
> > exe a : a.cpp lib1 lib2 ;
> >
> > usage requirements brought by lib1 might well affect some conditional 
> > requirements
> > in lib2, and in order to figure out the final properties for all targets 
> > you potentially need
> > to take multiple passed though all targets, re-computing usage 
> > requirements and propagating
> > all the way up and down. I never had time or motivation to spell down such 
> > an algorithm.
> 
> So, what does it mean in  a context of forcing Boost.Test users to employ 
> asynch exceptions?

It means that you have two choices:

        1. Just document that Boost.Test users should enable
        asynch exceptions and hope they'll do that.
        2. Implement a mechanism that will error out if Boost.Test
        is used with async-exceptions not set.

(2) is possible, but is a bit tricky, so probably not for 1.34.

- Volodya