predeclaring subs problems

leocharre has asked for the wisdom of the Perl Monks concerning the following question:

a.pm:

package A;
use vars qw{$VERSION @ISA @EXPORT @EXPORT_OK};
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(&a);
use strict;

sub a;

sub a {
 $a = $_[0];
 defined $a or $a='a';
 print $a;
}

1;
[download]

The following use of A.pm works fine. script.cgi

#!/usr/bin/perl -Tw
use lib 'where/a/pm/resides';
use strict;
use A;

a;

exit;
[download]

However, if I add another module that uses A.pm's b subroutine..
B.pm:

package B;
use vars qw{$VERSION @ISA @EXPORT @EXPORT_OK};
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(&b);
use strict;
use A;

sub b;

sub b {
 a;
}

1;
[download]

And make use of this...
script2.cgi

#!/usr/bin/perl -Tw
use lib 'where/a/pm/resides';
use strict;
use A;
use B;

a;

b;

exit;
[download]

I get an error on b.. that it's a bareword. But- why? I can turn the call as &b; and it will work, but.. why didn't a need that ? I tried doing use A on B.pm, but it makes no diff- I am so missing something here. What is it?

I read that if you predeclare a sub then you don't need to use () to pass args, do I need to predeclare a sub somewhere else ?

Comment on predeclaring subs problems Select or Download Code

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Re: predeclaring subs problems by ikegami (Patriarch) on Mar 17, 2006 at 20:49 UTC
I don't get the error you describe until I remove the `use lib`. Without the `use lib`, the code module "B" is loaded instead of your module "B". You get the error because the core module "B" doesn't export a function called "b". Rename your module from "B" to something else and you'll be fine.	[reply] [d/l] [select]
Re^2: predeclaring subs problems by leocharre (Priest) on Mar 19, 2006 at 20:44 UTC
Maybe I can ask this another way. Here is my module: `package Module; use strict; use Exporter; use vars qw{$VERSION @ISA @EXPORT @EXPORT_OK %EXPORT_TAGS}; $VERSION = '0.01'; @ISA = qw(Exporter); @EXPORT = qw(); @EXPORT_OK = qw(food cook); %EXPORT_TAGS = ( kitchen => [qw(food)], all => [qw(food cook)]); sub cook; sub food; cook { print "cooked $_[0]"; } food { my $food = $_[0]; defined $food or $food = 'apples'; print "$food is food"; } 1;` [download] My script using this module.. `use Module qw(:all); food('grapes'); food; # this works fine.` [download] However, when I have another module, that also has `use Module qw(:all);` [download] i get an error! `Undefined subroutine &Module::Module2::div called at /xxxxx/Module/Mod +ule2.pm line xxx` [download] I read that predeclaring a sub is what allows me to gove it arguments such as `food 'orange';` - This is making me a little loopy. I think what's going on here, since use runs once, the main script is immporting &food - an therefore any other modules that may want to call &food, will have to do so as &::food .. is that correct? How do I get &food to be inherited by all the code ? I guess is what i want..	[reply] [d/l] [select]
Re^3: predeclaring subs problems by ikegami (Patriarch) on Mar 20, 2006 at 15:36 UTC
First, don't post code you didn't run. You're missing the word "sub" in a couple of places. Secondly, since the error is in Module2, it would help if you could show it. I suspect you did `use Module qw(:all); package Module2; ... cook(); ...` [download] when you should have done `package Module2; use Module qw(:all); ... cook(); ...` [download] The former imports everything into the wrong package.	[reply] [d/l] [select]