Problem in using Exporter

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

Dear Monks,
I am facing some problems in compiling two modules which use one another and one of the module imports few methods exported by the other. You can find both modules below:

#=======================================
# First.pm
package First;

use strict;
use warnings;

use Second;

use Exporter;
our @EXPORT_OK = qw(first_method);

sub first_method {
    print "Inside first_method\n";
}
#===================================================
# Second.pm
package Second;

use strict;
use warnings;

use First qw(first_method);

sub second_method {
    print "Inside second_method\n";
    first_method();
}
#===================================================
[download]

When I compile First.pm (perl -wc First.pm), the compiler after looking at the line "use Second" should start compiling Second.pm. By the time the compiler compiles the line "use First qw(first_method)", First was not compiled yet and therefore First's @EXPORT_OK will be empty. So, the compilation should fail saying that first_method not exported by First. But, the compilation succeeds. Why?

Regards,
- Praveen.

Edit: g0n - code tags

Comment on Problem in using Exporter Download Code

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Re: Problem in using Exporter by mscharrer (Hermit) on Apr 21, 2008 at 14:34 UTC
Hi, I'm not sure where your "problem" is. You are missing an error not getting one. The solution is, I think, that Perl looks up the function names at run-time not at compile-time! The call to `first_method()` is compiled in but where/what this function exactly is is only interpreted at run-time, which isn't executed when using the -c switch. Also your code is incomplete because you are missing a main file which uses this two modules: `#!/usr/bin/perl use warnings; use strict; use Second; Second::second_method();` [download] When I run this script I get the following error: `Inside second_method Undefined subroutine &Second::first_method called at Second.pm line 11 +.` [download] But I figured out that you missed the following line in First.pm: `our @ISA = qw(Exporter);` [download] Otherwise nothing will be exported.	[reply] [d/l] [select]
Re^2: Problem in using Exporter by praveenkumar (Novice) on Apr 22, 2008 at 06:05 UTC
The import() method in Exporter class is executed at the compile-time by the use compiler directive. So, when the compiler sees use First qw(first_method) the Exporter class should look at EXPORT or EXPORT_OK of First and check for the method first_method. If it is not there in any of the EXPORT lists then it should throw an error. But it is not....	[reply]