In Perl 5, the difference between a function, a class method, a non-virtual method and a virtual method is entirely in the call.

Function call	foo(...)
Class method call	$class->foo(...)
Non-virtual method call (Hardcoded)	$o->Class::foo(...)
Non-virtual method call (Dynamic)	my $method = __PACKAGE__->can('foo'); $o->$method(...)
Virtual method call	$o->foo(...)

Needless to say, people only create virtual instance methods in Perl.

You're expected to use the correct calling convention for a given sub.