The defined interface decides which property to access based on the caller() function. Importing a method into a namespace (e.g. via Exporter) only creates an alias to the original, so any functions called from the method see the original namespace as the result of caller().

Example: $obj is of class MyClass. Depending on whether ego() is called from a native subroutine of MyClass (bar)or an imported subroutine from Plugin (foo), ego() finds a different calling package -- and thus returns a different storage hash. In the example below, foo() and bar both serve as accessors to the name field -- but they store/access different underlying hashes for the same object.

use strict;
use warnings;
no warnings qw/once/;

package Alter;

my %data;

sub ego {
    return( $data{scalar caller(0)} ||= {} );
}

package Plugin;

sub foo {
    $_[0]->ego()->{name} = $_[1] if @_ >  1;
    return $_[0]->ego()->{name};
}

package MyClass;

*ego = \&Alter::ego;
*foo = \&Plugin::foo;

sub bar {
    $_[0]->ego()->{name} = $_[1] if @_ >  1;
    return $_[0]->ego()->{name};
}

package main;

my $obj = bless( \my $scalar, "MyClass" );

$obj->bar( "Larry" );
$obj->foo( "Damian" );

for my $m ( qw/bar foo/ ) {
    print "$m: ", $obj->$m, "\n";
}

[download]

Prints:

bar: Larry
foo: Damian

[download]

This would be reasonable behavior if MyClass was a subclass of Plugin and both classes defined a name field, but that isn't what's happening here.

-xdg

Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

In reply to Re^9: Beyond Inside-Out by xdg
in thread Beyond Inside-Out by Anno

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.