עידו פרלמוטר (Ido Perlmuter)

NAME

Homer - Simple prototype-based object system

SYNOPSIS

        use Homer;

        # create a prototype object
        my $person = Homer->new(
                first_name => 'Generic',
                last_name => 'Person',
                say_hi => sub {
                        my $self = shift;
                        print "Hi, my name is ", $self->first_name, ' ', $self->last_name, "\n";
                }
        );

        # create a new object based on it
        my $homer = $person->extend(
                first_name => 'Homer',
                last_name => 'Simpson'
        );

        $homer->say_hi; # prints 'Hi, my name is Homer Simpson'

        # let's extend even more
        my $bart = $homer->extend(
                first_name => 'Bart',
                father => sub { print "My father's name is ", $_[0]->prot->first_name, "\n" }
        );

        $bart->say_hi; # prints 'Hi, my name is Bart Simpson'
        $bart->father; # prints "My father's name is Homer"

DESCRIPTION

Homer is a very simple prototype-based object system, similar to JavaScript. In a prototype based object system there are no classes. Objects are either directly created with some attributes and methods, or cloned from existing objects, in which case the object being cloned becomes the prototype of the new object. The new object inherits all attributes and methods from the prototype. Attributes and methods can be overridden, and new ones can be added. The new object can be cloned as well, becoming the prototype of yet another new object, thus creating a possibly endless chain of prototypes.

Prototype-based objects can be very powerful and useful in certain cases. They can provide a quick way of solving problems. Plus, sometimes you just really need an object, but don't need a class. I like to think of prototype-based OO versus class-based OO as being similar to schema-less database systems versus relational database systems.

Homer is a quick and dirty implementation of such a system in Perl. As Perl is a class-based language, this is merely a hack. When an object is created, Homer creates a specific class just for it behind the scenes. When an object is cloned, a new class is created for the clone, with the parent object's class pushed to the new one's @ISA variable, thus providing inheritance.

I can't say this implementation is particularly smart or efficient, but it gives me what I need and is very lightweight (Homer has no non-core dependencies). If you need a more robust solution, Class::Prototyped might fit your need.

HOMER AT A GLANCE

  • Prototypes are created by calling new() on the Homer class with a hash, holding attributes and methods:

            my $prototype = Homer->new(
                    attr1 => 'value1',
                    attr2 => 'value2',
                    meth1 => sub { print "meth1" }
            );
    
            $prototype->attr1; # value1
            $prototype->attr2; # value2
            $prototype->meth1; # prints "meth1"
  • A list of all pure-attributes of an object (i.e. not methods) can be received by calling attributes() on the object.

            $prototype->attributes; # ('attr1', 'attr2')
  • Every object created by Homer can be cloned using extend( %attrs ). The hash can contain new attributes and methods, and can override existing ones.

            my $clone = $prototype->extend(
                    attr2 => 'value3',
                    meth2 => sub { print "meth2" }
            );
    
            $clone->attr1; # value1
            $clone->attr2; # value3
            $clone->meth1; # prints "meth1"
            $clone->meth2; # prints "meth2"
  • Objects based on a prototype can refer to their prototype using the prot() method:

            $clone->prot->attr2; # value2
  • All attributes are read-write:

            $clone->attr1('value4');
            $clone->attr1; # value4
            $clone->prot->attr1; # still value1
  • New methods can be added to an object after its construction. If the object is a prototype of other objects, they will immediately receive the new methods too.

            $prototype->add_method('meth3' => sub { print "meth3" });
            $clone->can('meth3'); # true
  • New attributes can't be added after construction (for now).

  • Cloned objects can be cloned too, creating a chain of prototypes:

            my $clone2 = $clone->extend;
            my $clone3 = $clone2->extend;
            $clone3->prot->prot->prot; # the original $prototype

CONSTRUCTOR

new( [ %attrs ] )

Creates a new prototype object with the provided attributes and methods (if any).

CONFIGURATION AND ENVIRONMENT

Homer requires no configuration files or environment variables.

DEPENDENCIES

None other than Carp.

BUGS AND LIMITATIONS

Please report any bugs or feature requests to bug-Homer@rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Homer.

SUPPORT

You can find documentation for this module with the perldoc command.

        perldoc Homer

You can also look for information at:

AUTHOR

Ido Perlmuter <ido@ido50.net>

LICENSE AND COPYRIGHT

Copyright 2017 Ido Perlmuter

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.