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

From: Gennadiy Rozental (gennadiy.rozental_at_[hidden])
Date: 2006-12-17 04:41:46

"Vladimir Prus" <ghost_at_[hidden]> wrote in message 
news:200612170121.33251.ghost_at_cs.msu.su...
> On Sunday 17 December 2006 01:04, David Abrahams wrote:
>> Roland Schwarz <roland.schwarz_at_[hidden]> writes:
>>
>> > The test library specifies in its requirements:
>> >
>> > <toolset>msvc:<asynch-exceptions>on
>> >
>> > Now when I try to put this also into the usage-requirements, and try to
>> > build something that uses the test library Boost.Build complains with:
>> >
>> > 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?

Gennadiy