# Generated by Pod::WikiDoc version 0.18

=pod

=head1 NAME

Class::InsideOut::Manual::About - guide to this and other implementations of the
inside-out technique

=head1 VERSION

This documentation refers to version 1.09

=head1 DESCRIPTION

This manual provides an overview of the inside-out technique and its
application within C<<< Class::InsideOut >>> and other modules.  It also provides a
list of references for further study.

=head2 Inside-out object basics

Inside-out objects use the blessed reference as an index into lexical data
structures holding object properties, rather than using the blessed reference
itself as a data structure.

  $self->{ name }        = "Larry"; # classic, hash-based object
  $name{ refaddr $self } = "Larry"; # inside-out

The inside-out approach offers three major benefits:

=over

=item *

Enforced encapsulation: object properties cannot be accessed directly
from ouside the lexical scope that declared them

=item *

Making the property name part of a lexical variable rather than a hash-key
means that typos in the name will be caught as compile-time errors (if
using L<strict>)

=item *

If the memory address of the blessed reference is used as the index,
the reference can be of any type

=back

In exchange for these benefits, robust implementation of inside-out
objects can be quite complex.  C<<< Class::InsideOut >>> manages that complexity.

=head2 Philosophy of C<<< Class::InsideOut >>>

C<<< Class::InsideOut >>> provides a set of tools for building safe inside-out classes
with maximum flexibility.

It aims to offer minimal restrictions beyond those necessary for robustness of
the inside-out technique.  All capabilities necessary for robustness should be
automatic.  Anything that can be optional should be.  The design should not
introduce new restrictions unrelated to inside-out objects, such as attributes
and C<<< CHECK >>> blocks that cause problems for C<<< mod_perl >>> or the use of source
filters for syntatic sugar.

As a result, only a few things are mandatory:

=over

=item *

Properties must be based on hashes and declared via C<<< property >>>

=item *

Property hashes must be keyed on the C<<< Scalar::Util::refaddr >>>

=item *

C<<< register >>> must be called on all new objects

=back

All other implementation details, including constructors, initializers and
class inheritance management are left to the user (though a very simple
constructor is available as a convenience).  This does requires some additional
work, but maximizes freedom.  C<<< Class::InsideOut >>> is intended to be a base class
providing only fundamental features.  Subclasses of C<<< Class::InsideOut >>> could be
written that build upon it to provide particular styles of constructor,
destructor and inheritance support.

=head2 Other modules on CPAN

=over

=item *

L<Object::InsideOut> -- This is perhaps the most full-featured, robust
implementation of inside-out objects currently on CPAN.  It is highly
recommended if a more full-featured inside-out object builder is needed.
Its array-based mode is faster than hash-based implementations, but black-box
inheritance is handled via delegation, which imposes certain limitations.

=back

=over

=item *

L<Class::Std> -- Despite the name, this does not reflect currently known best
practices for inside-out objects.  Does not provide thread-safety with CLONE
and doesn't support black-box inheritance.  Has a robust
inheritanceE<sol>initialization system.

=back

=over

=item *

L<Class::BuildMethods> -- Generates accessors with encapsulated storage using
a flyweight inside-out variant. Lexicals properties are hidden; accessors must
be used everywhere. Not thread-safe.

=back

=over

=item *

L<Lexical::Attributes> -- The original inside-out implementation, but missing
some key features like thread-safety.  Also, uses source filters to provide
Perl-6-like object syntax. Not thread-safe.

=back

=over

=item *

L<Class::MakeMethods::Templates::InsideOut> -- Not a very robust
implementation. Not thread-safe.  Not overloading-safe.  Has a steep learning
curve for the Class::MakeMethods system.

=back

=over

=item *

L<Object::LocalVars> -- My own original thought experiment with 'outside-in'
objects and local variable aliasing. Not safe for any production use and offers
very weak encapsulation.

=back

=head2 References for further study

Much of the Perl community discussion of inside-out objects has taken place on
Perlmonks (L<http://perlmonks.org>).  My scratchpad there has a fairly
comprehensive list of articles
(L<http://perlmonks.org/index.pl?node_id=360998>).  Some of the more
informative articles include:

=over

=item *

Abigail-II. "Re: WhereE<sol>When is OO useful?". July 1, 2002.
L<http://perlmonks.org/index.pl?node_id=178518>

=item *

Abigail-II. "Re: Tutorial: Introduction to Object-Oriented Programming".
December 11, 2002. L<http://perlmonks.org/index.pl?node_id=219131>

=item *

demerphq. "Yet Another Perl Object Model (Inside Out Objects)". December 14,
2002. L<http://perlmonks.org/index.pl?node_id=219924>

=item *

xdg. "Threads and fork and CLONE, oh my!". August 11, 2005.
L<http://perlmonks.org/index.pl?node_id=483162>

=item *

jdhedden. "Anti-inside-out-object-ism". December 9, 2005.
L<http://perlmonks.org/index.pl?node_id=515650>

=back

=head1 SEE ALSO

=over

=item *

L<Class::InsideOut>

=item *

L<Class::InsideOut::Manual::Advanced>

=back

=head1 AUTHOR

David A. Golden (DAGOLDEN)

=head1 COPYRIGHT AND LICENSE

Copyright (c) 2006, 2007 by David A. Golden

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 
LE<lt>http:E<sol>E<sol>www.apache.orgE<sol>licensesE<sol>LICENSE-2.0E<gt>

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.


