Re: New conditional assignment facility

[Alejandro Colomar]

Hi Paul,

On 1/11/24 14:38, Paul Smith wrote:
> On Thu, 2024-01-11 at 14:28 +0100, Alejandro Colomar wrote:
> > > >         alx@debian:~/tmp$ cat Makefile
> > > >         var ?= foo
> > > >         var ?+= bar
> > > >         $(info $(var))
> > > >         alx@debian:~/tmp$ make-9000
> > > >         foo bar
> > > >         make: *** No targets.  Stop.
> > > >         alx@debian:~/tmp$ make-9000 var=foo
> > > >         foo
> > > >         make: *** No targets.  Stop.
> > > >         alx@debian:~/tmp$ var=foo make-9000
> > > >         foo
> > > >         make: *** No targets.  Stop.
>
> Sorry Alejandro; maybe you need to rewrite your examples again without
> all the corrections, because I don't understand what you mean.
>
> In all your examples, the value of var is set by the first line if it's
> not already set:
>
>      var ?= foo
>
> After this line, var will either be "foo" or it will be whatever value
> var had before that assignment (from the environment or command line or
> whatever, it doesn't matter).  But it's definitely defined.
>
> Once that happens, any subsequent "?" assignments, of any type, are
> simply ignored and useless because "?" means "set if not defined" but
> after the above line, var is always defined.

Hmm, after thinking about it again, I think my suggestion was dumb.

I was thinking of "?" meaning "set if not defined in the environment",
which is how I always used it.  But that's not what it means.

Cheers,
Alex

> So it doesn't matter if the next line is "var ?= bar" or "var ?+= bar"
> or whatever: it is just ignored.