On Wed, Jul 18, 2007 at 02:20:15PM +0900, Jack Minoshima wrote:
> Hi.
> Please allow me to ask another silly question.
>
> I wrote the program and it works fine.
>
> --------------------------------------------------------------------
> Animal.pm
> package Animal;
> use Exporter;
> @ISA = qw(Exporter);
> @EXPORT = qw(speak);
> sub speak {
> print "I speak!\n";
> }
> 1;
>
> ----------------------------------------------------------------------
> Mouse.pm
> package Mouse;
> use Animal;
> @ISA = qw(Animal);
> @EXPORT = qw(speak sound);
> sub sound {
> print "the sound!\n";
> };
> 1;
>
> ------------------------------------------------------------------------
> farm.pl
> use Mouse;
> speak;
> sound;
>
> C:\Documents and Settings\jackm\usetest>farm.pl
> I speak!
> the sound!
>
> but when I change Mouse.pm to replace "use Animal and set @ISA" with use
> base, it won't work.
> ----------------------------------------------------------------------
> Mouse.pm
> package Mouse;
> use base qw(Animal);
> @EXPORT = qw(speak sound);
> sub sound {
> print "the sound!\n";
> };
> 1;
>
> C:\Documents and Settings\jackm\usetest>farm.pl
> Can't call method "sound" on an undefined value at Animal.pm line 10.
>
> Please someone kindly let me know why?
Deriving from Exporter provides your package with an import() sub that
will export the symbols you have specified (perldoc Exporter).
"use" calls a module's import sub (perldoc -f use).
"use base" doesn't (perldoc base).
The purpose of "use base" is to establish a class hierarchy. OO doesn't
really fit well with exporting. In the real world, you will probably
need to pick a single paradigm and stick to it.
--
Paul Johnson - [EMAIL PROTECTED]
http://www.pjcj.net
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