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Re: New conditional assignment facility
From: |
Alejandro Colomar |
Subject: |
Re: New conditional assignment facility |
Date: |
Thu, 11 Jan 2024 14:22:19 +0100 |
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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- New append operators (was: Re: New conditional assignment facility), (continued)
- New append operators (was: Re: New conditional assignment facility), Paul Smith, 2024/01/28
- Re: New conditional assignment facility, Paul Smith, 2024/01/27
- RE: New conditional assignm ent facility, rsbecker, 2024/01/27
- Re: New conditional assignm ent facility, Paul Smith, 2024/01/27
- RE: New conditional assignm ent facility, rsbecker, 2024/01/27
- New append operators (was: Re: New conditional assignment facility), Paul Smith, 2024/01/28
- RE: New append operators (was: Re: New conditional assignment facility), rsbecker, 2024/01/28
- Re: New append operators (was: Re: New conditional assignment facility), Paul Smith, 2024/01/28
- Re: New conditional assignm ent facility, Edward Welbourne, 2024/01/29
- Re: New conditional assignment facility, Edward Welbourne, 2024/01/29
Re: New conditional assignment facility,
Alejandro Colomar <=