in reply to ifdef in modules

The limitation is not ifdef's, but -M's. use is block/file scoped. -M is the same thing as use at the top of the input file, therefore -M won't affect the module.

bla.pl
------
BEGIN { $|=1 }
use bla ();
$planet = "World\n";
print($planet);


bla.pm
------
$greet = "Hello\n";
print($greet);


>perl -Mstrict bla.pl
Hello
Global symbol "$planet" requires explicit package name at bla.pl line 
+3.
Global symbol "$planet" requires explicit package name at bla.pl line 
+4.
Execution of bla.pl aborted due to compilation errors.

[download]

As you can see, strict did not affect the module.

Replies are listed 'Best First'.
Re^2: ifdef in modules
by clee (Novice) on Jun 14, 2005 at 16:54 UTC

    The way ifdef seems to be implemented1, it does its thing before the compilation stage, so it's not quite the same as 'use strict'2.

    1 I say _seems_ to be implemented because I don't fully understand how it works. If I did, I'd know why it's not working :)

    2I'm not really sure how 'use strict' works either, so take that for what it's worth ;)

[reply]

      According to the ifdef docs:

      This version is completely written in Perl. It uses a source filter to provide its magic to the script being run and an @INC handler for all of the modules that are loaded otherwise.
      which says to me that we use an @INC handler to load modules. And the lib says it puts stuff at the front of the @INC. So it sounds to me like the two are not compatable with each other.

      A quick test shows that if you "use ifdef;" at the top of your module, whatever you put on the commandline will propogate... you may want to try more significant tests before relying on it, though.

[reply]

        Ok, it looks like I'll have to read up on how an @INC handler works (suggestions are welcome).

        In the meantime, as per your test, I put 'use ifdef;' at the top of the module, and the vars I pass on the commandline now propagate. Just to make sure I understand the significance of this, let me see if I've got this right:

        1. -Mifdef=DEBUGGING on the commandline puts a handler into @INC
        2. use lib './perl5lib'; in foo.pl puts perl5lib into @INC
        3. use ifdef; in Bar.pm puts another handler into @INC

        The last handler (added in step 3) can now get triggered because it is at the front of @INC. It also knows about perl5lib because it was added in step 2 before the triggered handler. It is also able to process the pod sections tagged with DEBUGGING because it was set in the original handler in step 1.

        Am I even close? All this playing with @INC is pretty new to me, so forgive my ignorance.

        Thanks!
[reply]

In Section Seekers of Perl Wisdom