Oh geez! I'm sorry, I forgot to mention David Nicol in the REFERENCES,
who also gave great input, especially on the BOOLEAN accessor. Thanks
David! I swear I'll put you in v2. :-{
-Nate
Perl6 RFC Librarian wrote:
This and other RFCs are available on the web at
http://dev.perl.org/rfc/
=head1 TITLE
True Polymorphic Objects
=head1 VERSION
Maintainer: Nathan Wiger [EMAIL PROTECTED]
Date: 25 Aug 2000
Mailing List: [EMAIL PROTECTED]
Version: 1
Number: 159
Status: Developing
=head1 ABSTRACT
Currently, using objects in numeric and string contexts is not very
useful or easy:
$r = new CGI;
$z = $r + $x; # oops
print "$r\n"; # double-oops
You can use facilities such as Ctie to help fix this issue, but Ctie
is limited and slow. You can also overload operators, but this is not
flexible enough for many applications since it applies to a package (and
not individual objects).
This RFC proposes the concept of Btrue polymorphic objects, which are
objects that can morph into numbers, strings, booleans, and much more
on-demand. As such, objects can be freely passed around and manipulated
without having to care what they contain (or even that they're objects).
=head1 DESCRIPTION
=head1 Overview
The top-level syntax remains the same. As such, transition to Perl 6 is
very smooth for most people, and in fact most users don't have to care
about any of the following details. To them, this script will "just
work":
$y = Math-data(7);
$x = 3;
$name = getname("Nate");
if ( $x 5 ) {
$y += $x;
if ( ! $name ) {
$name = "The math whiz";
}
}
print "$name got $y"; # "Nate got 10"
However, under the hood things might work drastically differently. In
fact, C$y and C$name might well be polymorphic objects:
$y = Math-data(7); # $y-CREATE, $y-STORE(7)
$x = 3; # $x = 3
$name = getname("Nate"); # $name-CREATE, $name-STORE("Nate")
if ( $x 5 ) { # $x 5
$y += $x; # $y-STORE($y-NUMBER-PLUS($x))
if ( ! $name ) { # $name || $name-BOOLEAN
$name = "The math whiz";# $name-STORE("...")
}
}
print "$name got $y";# $name-STRING , $y-STRING
Here, C$y and C$name are objects, but we don't have to care. These
objects have a key property: Icontext sensitivity. They have numerous
different methods which are each called only in specific instances. So,
being called in a numeric context calls CNUMBER, whereas being called
in a string context would call CSTRING.
Plus, operators are overloadable as well. This means that we might
decide to overload C+ to become a Java-like concatenation operator on
our objects:
$string = $name + "Wiger"; # $name-STRING-PLUS("Wiger")
Yuck. :-) But it can be done, and that's pretty cool.
=head2 Polymorphic Methods
The following are the proposed methods for Perl 6 objects. Note that
these methods are completely Ioptional for a class to define. If they
are not defined, the object would retain its current behavior. The hooks
are in Perl if you want them, otherwise they don't get in the way.
Note that CSTRING, CNUMBER, and CBOOLEAN are specialized forms of
CFETCH. If you define them, they are used instead of CFETCH in the
given context, otherwise CFETCH is used. Also note that the operators,
when overloaded, behave similarly to 'use overload', but on an
Iobject-by-object basis, rather than package-wide.
Data Conversion and Access
-
STRING Called in a string context
NUMBER Called in a numeric context
BOOLEAN Called in a boolean context
Operator Overloading
-
PLUS Called in + context
MINUSCalled in - context
TIMESCalled in * context
DIVIDED Called in / context
MODULUS Called in % context
NUMCMP Called in = context
NUMEQCalled in == context
NUMNECalled in != context
NUMLTCalled in context
NUMGTCalled in context
NUMLECalled in = context
NUMGECalled in = context
STRCMP Called in cmp context
STREQCalled in eq context
STRNECalled in ne context
STRLTCalled in lt context
STRGTCalled in gt context
STRLECalled in le context
STRGECalled in ge context
BITAND Called in context
BITORCalled in | context
BITXOR Called in ^ context
BITNOT Called in ~ context
Assignment and Existence
-
CREATE Called in object creation
STORECalled
