Re: New conditional assignm ent facility

[Paul Smith]

On Sat, 2024-01-27 at 15:52 -0500, rsbecker@nexbridge.com wrote:
> > I'm interested in peoples' opinions about which of these two
> > implementations they would feel to be more "intuitive" or
> > "correct".  Also please consider issues of "action at a distance"
> > where a variable is assigned in one makefile and appended to in
> > some other makefile, potentially far away.
> 
> Intuitive reading of this would seem that "bar=2 2 3" is better, as
> +:= should force complete resolution of the string applied to bar,
> not partial resolution of foo keeping an instance of $(foo) for
> resolution later.

Hm, maybe I'm just weird.  Or maybe I chose a poor example.

What if the example was like this:

  foo_ARGS = -a
  bar_ARGS = -b
  ARGS = $($@_ARGS) -x

  all: foo bar
  foo bar: ; cmd $(ARGS) $@

  ARGS +:= $(shell gen-args)

where the "gen-args" program outputs "-z".

and now the value of ARGS would either be "$($@_ARGS) -x -z" using the
method I was suggesting, or it would be " -x -z" using the alternative
method where ARGS was converted into a simple variable.

So using the first method make would run:

  cmd -a -x -z foo
  cmd -b -x -z bar

and using the alternative method make would run:

  cmd  -x -z foo
  cmd  -x -z bar

Is it still more intuitive?  Maybe the answer is "well, just don't do
that" :).  Or maybe "+!=" could be used in this specific situation, but
you get the idea.

The problem is that when you write the assignment +:= it's not always
so simple to know what the side-effects might be because you don't know
what the current behavior of the variable is, and it might change in
the future.  Of course, that's always a problem with makefiles.

-- 
Paul D. Smith <psmith@gnu.org>            Find some GNU make tips at:
https://www.gnu.org                       http://make.mad-scientist.net
"Please remain calm...I may be mad, but I am a professional." --Mad
Scientist