This and other RFCs are available on the web at http://dev.perl.org/rfc/ =head1 TITLE Operators: Polymorphic comparisons =head1 VERSION Maintainer: Damian Conway <[EMAIL PROTECTED]> Date: 7 Aug 2000 Last Modified: 18 Sep 2000 Mailing List: [EMAIL PROTECTED] Number: 54 Version: 2 Status: Frozen =head1 ABSTRACT This RFC proposes that numeric comparison operators default to stringwise comparison when both arguments are non-numeric strings. =head1 DESCRIPTION Currently the expression: "cat" == "dog" returns true. It is proposed that if I<neither> argument of a numeric comparison operator can be converted to a number, rather than both being converted to zero, the two operands should be compared using the equivalent stringwise comparison operator. It is further proposed that the current warning: Argument "%s" isn't numeric be changed to: Arguments of "%s" aren't numeric - using string comparison instead =head1 RATIONALE Perl has excellent support for generic programming, because of its dynamic typing, generic data types, and interface polymorphism. Just about the only place where that DWIM genericity breaks down is in comparisons. It is difficult to construct many generic algorithms and data structures in Perl, because there is no generic way to specify an ordering on dynamically typed data. For example, one cannot simply code a generic BST insertion method: sub insert { my ($self, $key, $value) = @_; if (!defined($self->{key})) { $self->{key} = $key; return $self->{value} = $value; } my $compare = $key <=> $self->{key}; return $self->{value} = $value unless $compare; $self->{$compare} = $self->new() unless $self->{$compare}; return $self->{$compare}->insert($key,$value); } This will work well for numeric keys, but fail miserably on most string-based keys, because <=> will generally return 0 for most pairs of strings. The above code would work correctly however if <=> detected the string/string comparison and automagically used cmp instead. =head1 IMPLEMENTATION Dammit, Jim, I'm a doctor, not an engineer! =head1 REFERENCES Chapter 12 of "Object Oriented Perl"
