NAME
Attribute::Overload::Match - argument-dependent handlers for overloaded
operators
DESCRIPTION
The module is a wrapper for overload, that provides a simple syntax for
calling different operator handlers for different passed arguments. The
idea is a curious ( but probably not a very practical ) mix of
Attribute::Overload and Sub::PatMat .
SYNOPSIS
use Attribute::Overload::Match;
Suppose we declare a class that overloads operations on integers:
sub new($) { my $x = $_[0]; bless \$x, __PACKAGE__ }
sub val($) { ${$_[0]} }
sub eq : op(==) { val(shift) == shift }
sub subtract : op(-) { new val(shift) - shift }
sub mul : op(*) { new val(shift) * shift }
sub add : op(+) { new val(shift) + shift }
sub qq : op("") { val(shift) }
sub le : op(<) { val(shift) < shift }
...
then we can change meaning of some operators with a touch of functional
style:
no warnings 'redefine';
sub fac : op(!,1) { new 1 }
sub fac : op(!) { !($_[0] - 1) * $_[0] }
or
sub fib : op(~,<2) { new 1 }
sub fib : op(~) { ~( $_[0] - 1) + ~($_[0] - 2) }
(if you don't like "no warnings 'redefine'", just use different sub
names for "fac" etc) thus
my $x = !new(10);
print "$x\n";
3628800
and
my $x = ~new(10);
print "$x\n";
89
SYNTAX
The only syntax available here is syntax that is passed to "op"
attributes, which is in general "sub mysub :
op(OPERATOR,CODE[,CODE[,CODE ...]])", where "OPERATOR" belongs to
strings defined in overload ( such as "+", "[]", "" etc), and "CODE"
strings are perl code, matching a parameter. However, for the sake of
readability, "CODE" can be also one of the following signatures:
Empty string
Parameter is never checked
String starting with a digit
Pataremeter must be defined and be equal ("==") to the value if the
string
Single-quoted string
Parameter must be defined and be equal ("eq") to the value if the
string
Non-quoted string beginning with a capital letter
The string defined as a class name. Parameter must be defined and be
an instance of the class (or its descendant).
"//"
Parameter must be defined.
One of "<,>,lt,gt,eq,==,ne,!=" followed by an expression
Parameter must be defined and return true when compared with the
expression using given comparison operator
Anything else
Anything else is passed directly to "eval" and is treated in a
boolean context thereafter.
ACKNOWLEDGEMENTS
Thanks to Anton Berezin for ideas on Sub::PatMat . Thanks to H. Merijn
Brandt for "//".
SEE ALSO
Attribute::Overload, Sub::PatMat, overload.
COPYRIGHT
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
AUTHOR
Dmitry Karasik <
[email protected]>
