Re: include files with :=

[Noel Yap]

Dill, John wrote:

> > I am still trying to track down where exactly my lag time is coming from, and it 
> > doesn't >appear to be from using the include directive by itself.  My question 
> > is how makefile
> > evaluates variables that are defined using ':=' with respect to include files.
> >
> > If I have a file include_me.mk which contains:
> >
> > my_var:=$(shell script)
> >
> > and I have included this file several times (indirectly through my file's 
> > dependent
> > include files).  Does make re-evaluate this variable assignment each time 
> > 'include
> > include_me.mk' appears?
> >
> > If that's the case, then I think that's where my problem is.
>
> I did some more investigation and found that this is where my performance 
> problem is.  It appears that time increases linearly with the number of times 
> the include file with ':=' variables are included, which means make is 
> evaluating it each time it is seen like it should.  Adding inclusion guards to 
> my include files should fix my performance problem.

This makes sense.  The := is evaluated at the time of the assignment (rather 
than at the time of usage as with =).  As Paul has said $(system) is an 
expensive call.

Noel