Re: [Boost-build] How to write a warn-once rule?

Subject: Re: [Boost-build] How to write a warn-once rule?
From: Juraj Ivanèiæ (juraj.ivancic_at_[hidden])
Date: 2013-02-11 18:49:05

On 11.2.2013. 23:47, Matthew Chambers wrote:
> I'm trying to write a rule like:
>
> rule warn-once ( once-flag ? : message )
> {
>       if ! $(once-flag)
>       {
> 	once-flag = true ;
>           echo $(message) ;
>       }
> }
>
> But it doesn't work because once-flag is passed by value. Is there a way to pass it by reference or
> a different way to approach this while still getting a simple interface?

I'd try something like this

rule warn-once ( warning-var )
{
     if ! $(.issued.$(warning-var))
     {
         ECHO $($(warning-var)) ;
     }
     else
     {
         ECHO Already issued! ;
     }
     .issued.$(warning-var) = true ;
}

.warning = WARNING TEXT ;

warn-once .warning ;
warn-once .warning ;

This approach has its problems, but might do the trick for you.