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Object::Extend - add and override per-object methods


    use Object::Extend qw(extend);

    my $foo1 = Foo->new;
    my $foo2 = Foo->new;

    extend $foo1 => {
        bar => sub { ... },

    $foo1->bar; # OK
    $foo2->bar; # error


This module allows objects to be extended with per-object methods, similar to the use of singleton methods in Ruby. Object methods are added to an object-specific shim class (known as an eigenclass), which extends the object's original class. The original class is left unchanged.



extend takes an object and a hash or hashref of method names and method values (coderefs) and adds the methods to the object's shim class. The object is then blessed into this class and returned.

It can be used in standalone statements:

    extend $object, foo => sub { ... }, bar => \&bar;

Or expressions:

    return extend($object => { bar => sub { ... } })->bar;

In both cases, extend operates on and returns the supplied object i.e. a new object is never created. If a new object is needed, it can be created manually e.g.:

    my $object2 = Object->new($object1);
    my $object3 = clone($object1);

    extend($object2, foo => sub { ... })->foo;
    return extend($object3 => ...);

Objects can be extended multiple times with new or overridden methods:

    # call the original method
    my $object = Foo->new;

    # override the original method
    extend $object, foo => sub { ... };

    # add a new method
    extend $object, bar => sub { ... };


This sub can optionally be imported to make the use of extend more descriptive. It takes and returns a hashref of method names/coderefs:

    use Object::Extend qw(extend with);

    extend $object => with { foo => sub { ... } };


Every extended object's shim class includes an additional (empty) class in its @ISA which indicates that the object has been extended. The name of this class can be accessed by importing the SINGLETON constant e.g.:

    use Object::Extend qw(SINGLETON);

    if ($object->isa(SINGLETON)) { ... } # object extended with object-specific methods





chocolateboy <>


Copyright (C) 2013 by chocolateboy

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.14.2 or, at your option, any later version of Perl 5 you may have available.