Re: [Boost-build] [bbv2] newbie: how to get value of a feature inside a rule

From: Vladimir Prus (ghost_at_[hidden])
Date: 2006-02-07 07:54:30

On Sunday 05 February 2006 14:31, Jaroslav Gresula wrote:
> Could someone advise me how to retrieve value of a feature within a
> rule? I followed an example from the docs which uses the toolset.flags
> rule but with no luck.
>
> Below is my attempt, but the TOOLSET variable expands to an empty string.
>
> ---
> local rule this-module-rule ( ) { return [ CALLER_MODULE ] ; }
> local this-module = [ this-module-rule ] ;
>
> import toolset ;
> toolset.flags $(this-module).print-toolset TOOLSET : <toolset> ;
>
> rule print-toolset ( )
> {
>    ECHO $(TOOLSET) ;
> }
>
> alias main : : [ print-toolset ] ;

This code is executed during Jamfile parsing stage. It calls the rule 
'print-toolset', that immediately executes "ECHO", but the value of 
$(TOOLSET) is empty, because it's only set when bjam starts executing 
actions, and only if 'print-toolset' is the updating action for some target.

Try this:

  import notfile ;
  import toolset ;
  import feature ;

  notfile test : @print-toolset ;

  rule print-toolset ( targets * : sources * : properties * )
  {
      ECHO "Toolset = " [ feature.get-values <toolset> : $(properties) ] ;
  }

Note that if you run "bjam" with two different toolsets, say:

    bjam gcc intel

you'll see two "Toolset = " lines, one for each time "test" is built.

You might also want to check the newly added FAQ item:

    http://boost.org/boost-build2/doc/html/bbv2/faq.html#id2577795

HTH,
Volodya