# prototypes only check arg format
# i.e. (scalar/array/hash/code/glob and number of args)

package Sample;
sub stringify () {
    return ($_[0]->{data}) x $_[1]
}

package main;
sub print_string($) {
    print $_[0]->stringify(1)
}

my $obj = bless ( {data=>"foo\n"}, 'Sample');
print_string($obj); # fine
print_string(5);    # uh oh... basic numbers don't have a stringify method,
                    # yet the arg passed the prototype since 5 is a scalar.