If the right side of the arrow is a scalar containing a reference
to a subroutine then this is equivalent to calling the referenced
subroutine directly with the class name or object on the left side
of the arrow as its first argument. No lookup is done and there is
no requirement that the subroutine be defined in any package related
to the class name or object on the left side of the arrow.

For example, the following calls to $display are equivalent:

    my $display = sub { my $self = shift; ... };
    $fred->$display("Height", "Weight");
    $display->($fred, "Height", "Weight");