{   package Base;
    sub x { ... }
}

{   package Child;
    our @ISA = 'Base';
    sub y { shift->x }
}

##</code><code>##

package Package;
sub y { shift->x }

##</code><code>##

{   package SomeRole;
    # Implementor must provide y
    sub y { shift->x }
}

{   package Class;
    our @ISA = 'SomeRole';
    sub x { ... }
}

##</code><code>##

sub some_method {
    my ($self, $arg) = @_
    ...
    $arg->other_method();
    ...
}

##</code><code>##

sub some_method {
    my ($self) = @_
    ...
    $self->attribute->other_method();
    ...
}