Class::InsideOut::Manual::About(3pm)			User Contributed Perl Documentation		      Class::InsideOut::Manual::About(3pm)

NAME

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

VERSION

       This documentation refers to version 1.10

DESCRIPTION

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

   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:

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

       o   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 strict)

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

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

   Philosophy of "Class::InsideOut"
       "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 "CHECK" blocks that cause problems for "mod_perl" or the use of source filters for syntatic
       sugar.

       As a result, only a few things are mandatory:

       o   Properties must be based on hashes and declared via "property"

       o   Property hashes must be keyed on the "Scalar::Util::refaddr"

       o   "register" must be called on all new objects

       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.  "Class::InsideOut" is
       intended to be a base class providing only fundamental features.  Subclasses of "Class::InsideOut" could be written that build upon it to
       provide particular styles of constructor, destructor and inheritance support.

   Other modules on CPAN
       o   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.

       o   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 inheritance/initialization system.

       o   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.

       o   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.

       o   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.

       o   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.

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

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

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

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

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

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

SEE ALSO

       o   Class::InsideOut

       o   Class::InsideOut::Manual::Advanced

AUTHOR

       David A. Golden (DAGOLDEN)

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 L<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.

perl v5.10.1							    2011-02-24				      Class::InsideOut::Manual::About(3pm)