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] }

   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 //.

COPYRIGHT

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

Dmitry Karasik <dmitry@karasik.eu.org>

CPAN RT