Re: [jamboost] Conditional sources?

From: Vladimir Prus (ghost_at_[hidden])
Date: 2003-03-14 02:14:15

Ali Azarbayejani wrote:
> Here's a simple question...can I do "Conditional Sources" using the same
> syntax as Conditional Properties?
>
> I.e.
>
> lib mylib : foo.cxx bar.cxx <os>NT:ntbase.cxx ;

No, it's not possible. Probably that would nicely rhyme with conditional 
properties, but some time ago Rene Rivera noted that conditional sources
can be achieved right now

alias platform-sources ;
alias platform-sources : a.cpp : <os>LINUX ;

exe hello : hello.cpp platform-sources ;

There are two alternatives for 'platform-sources' main target.
The first one is generic: it has any sources and produces nothing. The second 
is used only with <os>LINUX is properties and just returns all sources. So, 
on Linux, "a.cpp" will be compiled. On NT --- not. I attach a complete 
example. In the example, you can swithc <os>LINUX to <os>NT to see how it 
works.

A question how this method relates with conditional features now raises. I 
don't yet have an answer --- probably some experiments are needed.

> Or do I have to do something more convoluted like the following?
>
> Sources = foo.cxx bar.cxx ;
> if [ os.name ] = NT
> {
> Sources += ntbase.cxx ;
> }
> lib mylib : $(Sources) ;

That's an option too. I think I like "alternatives"-based variant better, 
though, especially because it's more flexible. For example, if Boost.Build
ever supports cross compiling, the if-based solution won't work anymore.
[ os.name ] will be host os name.

- Volodya
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