Re: [jamboost] Disallow free property in build request

From: Vladimir Prus (ghost_at_[hidden])
Date: 2002-07-10 11:26:44

David Abrahams wrote:
> I can't agree. For example, the maximum arity supported by Boost.Python can
> be adjusted by changing a #define. In theory this creates ODR violations,
> but in practice each individual user of the library can set this #define
> differenty for his own use. How would we support that?

I think it can be a free feature, but an ordinary one. I still can't 
understand how can we reasonable allow free features in build reqest.

exe a.exe : a.cpp biglibrary : <define>FOO ;

I hope you agree that <define>FOO should not be propagated to biglibrary. 
After all, we'd have no explicitly "propagated" features otherwise. Suppose 
build request is 

gcc <define>BAR ;

I think it's correct to say that applying requirements mean conceptually that 
we use the build request 

gcc <define>BAR <define>FOO 

to target without requirements. Then, how can we propagate the first define 
and not propagate the second?

> Answering my own question: one possibility might be that users write
> specific command-line option handling code in Jamfiles:
>
> --boost-python-max-arity=XXXX

With ordinary feature you'd have

boost-python-max-arity=XXXX

in the command line.

>
> Thoughts?
>
> ----- Original Message -----
> From: "Vladimir Prus" <ghost_at_[hidden]>
> To: <jamboost_at_[hidden]>
> Sent: Wednesday, July 10, 2002 11:59 AM
> Subject: [jamboost] Disallow free property in build request
>
> > I think that we should disallow free but non-propagated properties in
>
> build
>
> > request. The reason is that for example:
> >
> > exe a.exe : a.cpp biglibrary : <define>FOO ;
> >
> > Here, <define>FOO is not propagated to biglibrary, i.e. not used in its
> > building. Likewise, even if <define>BAZ is present in build request for
> > a.exe, it won't affect biglibrary. So, free properties in build request
>
> can
>
> > either
> > - affect the directly build targets
> > - affect nothing
> >
> > Both semantics are odd. Let's disallow free properties in build request
> > altogether.
>
>
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