use warnings;
use strict;

{ package Foo;
	use Data::Dump;
	use Scalar::Util qw/blessed/;
	sub new { return bless {}, shift }
	sub foo {
		my $self = shift if ref $_[0] eq __PACKAGE__;
		dd 'foo', $self, \@_;
	}
	sub bar {
		my $self = shift if defined blessed($_[0])
			&& $_[0]->isa(__PACKAGE__);
		dd 'bar', $self, \@_;
	}
}

{ package Bar;
	use parent -norequire, 'Foo';
}

Foo::foo('a');   # ("foo", undef, ["a"])
Foo::bar('b');   # ("bar", undef, ["b"])

my $f = Foo->new();
$f->foo('c');    # ("foo", bless({}, "Foo"), ["c"])
$f->bar('d');    # ("bar", bless({}, "Foo"), ["d"])

my $g = Bar->new();
$g->foo('e');    # ("foo", undef, [bless({}, "Bar"), "e"])  - oops!
$g->bar('f');    # ("bar", bless({}, "Bar"), ["f"])