Re: New conditional assignment facility

[Alejandro Colomar]

Hi Paul!

On Thu, Jan 11, 2024 at 01:44:19AM -0500, Paul Smith wrote:
> I've implemented a new capability for conditional assignments (not
> pushed yet).
> 
> After these changes, a "?" can precede any type of assignment
> operation, not just "=", and make it conditional (that is, it only
> takes effect if the variable is not already set).
> 
> So for example, in addition to "?=" which creates a recursive variable
> if the variable is not set yet, GNU Make will support "?:=" which
> creates a simple variable if the variable is not set yet.

Thanks!!

>  Of course if
> it's already set then the right-hand side of the assignment is not
> expanded.
> 
> Similarly the assignments "?::=" and "?:::=" are also supported.
> 
> 
> There is one question I wanted to ask for opinions on: what should we
> do with the "?+=" operator?

There's a use for it:  appending to a variable if it wasn't set in the
environment (ignoring what happened in the Makefile).

Here's what += does:

        alx@debian:~/tmp$ cat Makefile 
        var ?= foo
        var += bar
        $(info $(var))
        alx@debian:~/tmp$ make
        foo bar
        make: *** No targets.  Stop.
        alx@debian:~/tmp$ make var=foo
        foo
        make: *** No targets.  Stop.
        alx@debian:~/tmp$ var=foo make
        foo bar
        make: *** No targets.  Stop.

And here's what ?+= could do:

        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.

In the last case (environment variable), since var was set, ?+= would do
nothing, unlike +=.

Have a lovely day,
Alex

-- 
<https://www.alejandro-colomar.es/>
Looking for a remote C programming job at the moment.

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