Re: [Boost-build] How to select a source file by <target-os>

From: Jurko Gospodnetić (jurko.gospodnetic_at_[hidden])
Date: 2008-07-22 09:20:17

   Hi Jonathan.

> I want to select a source file based on the value of <target-os>, but it 
> seems rather unsatisfying to have to write an alias rule for each os I 
> support.
> 
> I've figured out that I can do this:
> 
> os-names = [ modules.peek builtin : .os-names ] ;
> 
> for local os in $(os-name)
> {
>     alias target-os-source : foo-$(os).cpp : <target-os>$(os) ;
> }
> 
> which saves some typing or cut & paste errors, but that's still rather 
> unsatisfying.
> 
> Seems to me there ought to be a better way, but I haven't found one yet.
> 

   Well your solution seems quick good to me :-) and could be trimmed 
down to (also avoids a typo in the original example):

> for local os in [ modules.peek builtin : .os-names ]
> {
>     alias target-os-source : foo-$(os).cpp : <target-os>$(os) ;
> }

   But IME most often you do not have the same files on different OS's 
and then it is more useful to actually have a separate alias alternative 
for each OS.

   There is also the option of providing the source file names lazily 
using indirect conditional requirements (see 
http://www.boost.org/doc/tools/build/doc/html/bbv2/advanced/targets.html#bbv2.advanced.targets.requirements) 
and the <source> property. Something like (warning: untested code):

> rule add-os-specific-sources ( properties * )
> {
>     local target-os = [ MATCH "^<target-os>(.*)$" : $(properties) ] ;              
>     return
> 	$(target-os)-specific-source-1
> 	$(target-os)-specific-source-2
> 	$(target-os)-specific-source-3
> 	$(target-os)-specific-source-4
> 	$(target-os)-specific-source-5 ;
> }
> 
> exe my-exe
>     :
>         some-fixed-source-1
>         some-fixed-source-2
>         some-fixed-source-3
>     :
>         <conditional>@add-os-specific-sources ;

   I guess what you would really like would be something like:

exe my-exe
     :
         some-fixed-source-1
         some-fixed-source-2
         some-fixed-source-3
        {target-os}-specific-source-1
        {target-os}-specific-source-2
        {target-os}-specific-source-3
        {target-os}-specific-source-4
        {target-os}-specific-source-5 ;

   and have Boost Build dynamically construct the source file names fotr 
you, but I don't think that is possible with the current Boost Build. 
But if you can define a clear and robust syntax for achieving this 
effect feel free to suggest it on the list.

   Hope this helps.

   Best regards,
     Jurko Gospodnetić