Hi sachinz2,

Packages can be declared (nearly) anywhere. A package declaration changes the current package name/namespace, and the new namespace is independent of the previous one, even if it's declared "within" another package - except that the two lexical scopes can overlap. In the case of OO, names do not matter - a class/package named "Foo::Bar" is not automatically related to "Foo" in any way, nor is a class/package declared within another class/package automatically related to its outer class, again except in the lexical scope (note that normal sub definitions/calls don't cross the package boundary via the lexical scope, as shown in the example below). The only way to establish an OO relationship is via @ISA and its helpers like base and parent. I'd suggest you have a look at package as well as "Packages" and "Symbol Tables" in perlmod, and then have a look at this example:

#!/usr/bin/env perl
use warnings;
use strict;

our $pack = __PACKAGE__; # $main::pack
print "$pack\n";         # prints "main"

package Foo;
our $pack = __PACKAGE__; # $Foo::pack
print "$pack\n";         # prints "Foo"

package Bar;
our $pack = __PACKAGE__; # $Bar::pack
print "$pack\n";         # prints "Bar"
yak();                   # defined below, prints "yak: Bar"

package Foo::Bar;
our $pack = __PACKAGE__; # $Foo::Bar::pack
print "$pack\n";         # prints "Foo::Bar"
sub yak {                # Foo::Bar::yak()
    print "yak: ".__PACKAGE__."\n" }
yak();                   # prints "yak: Foo::Bar"

{ package Foo;
    # now back to package "Foo", nested in a new block
    our $blah = __PACKAGE__; # $Foo::blah
    print "$blah\n";         # prints "Foo"
    print "$Foo::pack\n";    # $Foo::pack is still "Foo"
    print "$Bar::pack\n";    # and $Bar::pack is still "Bar"
    # however, "$pack" access the most recent lexical definition
    print "$pack\n"; # so this is actually $Foo::Bar::pack, "Foo::Bar"
    # yak(); # but this doesn't work, there is no Foo::yak!
    
    { package Bar; # and back in package "Bar"
        # but we're still in the most recent lexical scope
        print "$pack\n"; # so this is still $Foo::Bar::pack, "Foo::Bar
+"
        print "$blah\n"; # and this is still $Foo::blah, "Foo"
        sub yak {        # Bar::yak()
            print "yak: ".__PACKAGE__."\n" }
        yak();           # prints "yak: Bar"
    }
}

[download]

If you have further questions, I'd suggest you ask them with code to illustrate your question (see for example Short, Self Contained, Correct Example and How do I post a question effectively?).

Hope this helps,
-- Hauke D

Updated: Minor updates to wording for clarification.

In reply to Re: Understanding a OOP Code: Package declared within a Package by haukex
in thread Understanding a OOP Code: Package declared within a Package by sachinz2

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