package Foo;
sub new { bless {}, shift }
sub foo {
    my $self = shift;
    if (ref $self) {
        print "Instance method called on $self\n";
    }
    else {
        print "Class method called on class $self\n";
    }
}

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

package main;
Foo->foo;       # "Class method called on class Foo"
Foo->new->foo;  # "Instance method called on Foo=HASH(0x...)"
Bar->foo;       # "Class method called on class Bar"
Bar->new->foo;  # "Instance method called on Bar=HASH(0x...)"