# PODNAME: Class::InsideOut::Manual::About
# ABSTRACT: guide to this and other implementations of the inside-out technique
__END__
=pod
=encoding UTF-8
=head1 NAME
Class::InsideOut::Manual::About - guide to this and other implementations of the inside-out technique
=head1 VERSION
version 1.14
=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 outside 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 syntactic 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 Golden <dagolden@cpan.org>
=head1 COPYRIGHT AND LICENSE
This software is Copyright (c) 2006 by David A. Golden.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004
=cut