package MyPackage;

sub foo() { print 'stuff'; }

1;

MyPackage::foo();
MyPackage->foo();

##</code><code>##

package MyPackage;

sub foo() { 
     my $self = shift;
     my $text;

     if (ref($self) eq __PACKAGE__) {
         $text = shift;
     } else {
         $text = $self;
     };

     print $text;

};

1;

MyPackage::foo('stuff');
MyPackage->foo('stuff');