Module Inheritance

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

Well bretheren I'm in a bit of a pickle! I'm writing my first Perl Module and though it is working there is a small but irritating problem! My module called Hoos has several house-keeping related subroutines in it. In an ordinary script I have "use Hoos ;" and a call to one of the subs Hoos::mail_log(params). This works fine but I would prefer to omit the Hoos:: from the call. To this end I've included the following -

use Exporter ;
our @ISA = qw(Exporter)
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in the Hoos.pm code. My script now fails as a result of "an undefined routine main::mail_log" being called. Next I changed the Hoos.pm code to include -

package Hoos ;
our @EXPORT = qw( list of subs mail_log mail end_it etc) ;
use Exporter ;
our @ISA = qw(Exporter);
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All of which was lifted from the Perl Objects References & Modules manual. None of this has made a blind bit of a difference, the only way I can call any of the subs in Hoos.pm is to prefix the routine name by Hoos:: - can anyone tell me how to fix this.

Cheers,
Ronnie "Novice" Cruickshank

PS I don't pretend to understand the Exporter/Import business yet so don't presume I know very much!

edit (broquaint): added formatting

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Re: Module Inheritance by Abigail-II (Bishop) on Apr 29, 2004 at 12:40 UTC
`package Hoos; use Exporter (); our @ISA = qw /Exporter/; our @EXPORT = qw /mail_log/;` [download] ought to work. Abigail	[reply] [d/l]
Re: Module Inheritance by broquaint (Abbot) on Apr 29, 2004 at 12:44 UTC
You may need to demonstrate more code as that should work fine e.g `shell> cat Hoos.pm package Hoos; our @EXPORT = 'testsub'; use Exporter; our @ISA = 'Exporter'; sub testsub { print "exported testsub() ok\n" } 1; shell> perl -e 'use Hoos; testsub()' exported testsub() ok` [download] So there we've set up `Exporter` to export `testsub` whenever `Hoos` is `use`d. Also, you should `require Exporter` as `use`ing it calls its own `import` method. HTH `_________ broquaint`	[reply] [d/l]
Re: Module Inheritance by Abigail-II (Bishop) on Apr 29, 2004 at 13:00 UTC
So there we've set up Exporter to export testsub whenever Hoos is used. Also, you should require Exporter as useing it calls its own import method. A populair belief, but not true. Sure, using 'require' prevents the import() method to be called, but that's not the only way. `use Exporter (); # Don't call import!` [download] Less characters to type, and it gets dealt with at compile time. Why bother with require? Abigail	[reply] [d/l]
Re: Re: Module Inheritance by broquaint (Abbot) on Apr 29, 2004 at 13:36 UTC
A populair belief, but not true. Well, it is true. You know that. It doesn't magically not call `import`. Less characters to type, and it gets dealt with at compile time. Why bother with require? It's one less character to type and in modules the likes of `require Exporter` are being implicitly being handled at compile-time anyhow (assuming they've been `use`ed). As for the 'Why', force of habit I guess. I generally do `use Module ()` if I don't want `import` to be invoked but make an exception for `require Exporter`. C'est la vie. HTH `_________ broquaint`	[reply]
Re: Module Inheritance by Abigail-II (Bishop) on Apr 29, 2004 at 13:42 UTC
Re: Re: Module Inheritance by broquaint (Abbot) on Apr 29, 2004 at 14:05 UTC
Some notes below your chosen depth have not been shown here
Re: Module Inheritance by gellyfish (Monsignor) on Apr 29, 2004 at 12:45 UTC
Well the code as in your second attempt shoulod (indeed does in a small test.) work fine. There must be something you are not showing us here - are you doing 'use Hoos;' or 'require Hoos;' as the latter will not call Hoos::import() (which you inherited from Exporter) and thus will not work. Can you show us a cut down version of your code that exhibits this behaviour? /J\	[reply]
Re: Module Inheritance by matija (Priest) on Apr 29, 2004 at 12:42 UTC
I have a feeling that this is one of the places where the order of the statements matters. Move the `@EXPORT` assignement after the `@ISA` declaration in your code, and see if that helps.	[reply]