oracular (3) Class::InsideOut::Manual::About.3pm.gz

Provided by: libclass-insideout-perl_1.14-3_all bug

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


VERSION
       version 1.14


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:

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

       •   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)

       •   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 syntactic sugar.

       As a result, only a few things are mandatory:

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

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

       •   "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
       •   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.

       •   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.

       •   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.

       •   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.

       •   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.

       •   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:

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

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

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

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

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


SEE ALSO
       •   Class::InsideOut

       •   Class::InsideOut::Manual::Advanced


AUTHOR
       David Golden <dagolden@cpan.org>


       This software is Copyright (c) 2006 by David A. Golden.

       This is free software, licensed under:

         The Apache License, Version 2.0, January 2004