Re: [MacPerl] Simple Explanation for @ISA?

[Matthias Ulrich Neeracher <neeri@iis.ee.ethz.ch>]

Robert Ke <rke@qualcomm.com> writes:
>Sorry to tell you, the @ISA has something to do with OOP.  

It's actually even more confusing than that: While the @ISA mechanism often is
used for OOP, it is not strictly related to it. You can do OOP without @ISA and
use @ISA without OOP.

>It works like the @INC array which stores directories for perl  to search 
>for files in other directories.
>
>@ISA array contains names of classes so Perl could search for methods in 
>other classes.

So far, the explanation is correct (and quite elegant, too). However, your
terminology is more OOP biased than Perl itself in fact is. A more accurate
statement would be:

The @ISA array contains names of *modules* so Perl can search for *subroutines*
in other *modules*.

Stated this way, it becomes clear that @ISA works for OOP, but it also works
without OOP. Some important examples are:

@ISA = qw(Exporter) : All modules which export names do this. A statement such
    as "use xxx(a b c)" causes a subroutine named "import" to be executed, and
    this subroutine is taken from the "Exporter" module.

@ISA = qw(DynaLoader) : All Mac toolbox modules do this to be able to
     dynamically load code fragments (This is done in the "bootstrap" routine).

@ISA = qw(AutoLoader) : This can be used to split up modules and load pieces
     on demand.

Matthias

-----
Matthias Neeracher   <neeri@iis.ee.ethz.ch>   http://www.iis.ee.ethz.ch/~neeri
  "If people are boasting that they use the best tools, you can figure that 
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