In PHP, there was a major change in the object model between version 4 and version 5. This code here - incredibly - runs differently on the two versions and what happens when you assign an object to another variable has changed.


In PHP 4, the object being assigned is duplicated, so that if you change the original object after doing the assignment, then look up a property in the copy, you'll be given the value that you started with


In PHP 5, the new variable is just an extra name (an alias, if you like) for the original variable, so that if you change the original object after doing the assignment, in reality you're changing both. So that when you look up a property in the copy, you'll be given the value that you have just set in the original


This (and other entries this morning) are taken from the board examples I wrote during last Friday's Object Oriented Programming in PHP course. Each day during training, I'll draw dozens of diagrams to help delegates understand what's going on, and when asked I'm happy to document and publish some of them here. Bookings on our public courses are open - in other words, we'll accept bookings and welcome delegates who want to learn what we teach from any company or organisation, contractors, and private individuals. The prerequisites?
  • A desire to learn
  • A good understanding of the language in which the course is presented
  • For advanced courses - enough technical background / prior knowledge to be able to gain from the course (and to not hold up other delegates)
There's a full list of our public courses for the rest of the year at http://www.wellho.net/course/index.html - we have beginner and advanced course in PHP ... and also Linux, Java, Perl, Python, MySQL, Lua, C, Tcl, C++ and Ruby.
(written 2009-05-11, updated 2009-05-12)

 H108 - Objects in PHP
  [3211] Computer Graphics in PHP - World (incoming data) to Pixel (screen) conversion - (2011-03-24)
  [3210] Catchable fatal error in PHP ... How to catch, and alternative solutions such as JSON - (2011-03-22)
  [3142] Private and Public - and things between - (2011-01-22)
  [2922] Getting the OO design write - with PHP a example - (2010-08-14)
  [2921] Does copying a variable duplicate the contents? - (2010-08-14)
  [2774] PHP - Object Oriented Design in use - (2010-05-21)
  [2741] What is a factory? - (2010-04-26)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2680] Static class members in PHP - a documented example - (2010-03-16)
  [2641] Object Oriented Programming in PHP - (2010-02-19)
  [2632] Shipping a test harness with your class in PHP - (2010-02-12)
  [2435] Serialization - storing and reloading objects - (2009-10-04)
  [2434] Abstract classes, Interfaces, PHP and Java - (2009-10-03)
  [2380] Object Oriented programming - a practical design example - (2009-08-27)
  [2171] Cleaning up redundant objects - (2009-05-11)
  [2169] When should I use OO techniques? - (2009-05-11)
  [2160] PHP - getclass v instanceof - (2009-05-07)
  [1925] Introduction to Object Oriented Programming - (2008-12-06)
  [1820] Sorting objects in PHP - (2008-10-04)
  [1819] Calling base class constructors - (2008-10-03)
  [1682] Accounts in PHP - an OO demo - (2008-06-19)
  [1535] OO PHP demonstration - comparing objects and more - (2008-02-08)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [1153] Object Oriented Model - a summary of changes from PHP4 to PHP5 - (2007-04-18)
  [1027] Cue the music, I'm happy. - (2007-01-09)
  [836] Build on what you already have with OO - (2006-08-17)
  [720] Planning a hotel refurb - an example of a Gant chart in PHP - (2006-05-14)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [485] North, Norther and Northest - PHP 5 Objects - (2005-11-04)
  [421] Don't repeat code - use loops or functions - (2005-08-21)
  [343] Should I use structured or object oriented? - (2005-06-10)
  [205] PHP5 lets you say no - (2005-02-07)
  [124] PHP v Java - (2004-11-20)
  [67] Object Oriented Programming in PHP - (2004-09-29)

S159 - MySQL 5 and PHP 5
  [3455] MySQL, MySQLi, PDO or something else - how best to talk to databases from PHP - (2011-09-24)
  [1766] Diagrams to show you how - Tomcat, Java, PHP - (2008-08-22)
  [1754] Upgrade from PHP 4 to PHP 5 - the TRY issue - (2008-08-15)
  [1455] Connecting to MySQL 5 from PHP on Mac OSX Leopard - (2007-12-03)
  [1417] What software version do we teach? - (2007-10-31)
  [1131] MySQL - Password security (authentication protocol) - (2007-04-02)
  [515] MySQL - an FAQ - (2005-12-03)
  [494] MySQL - a score of things to remember - (2005-11-12)
  [104] mysql_connect or mysql_pconnect in PHP? - (2004-10-30)

Back to Cleaning up redundant objects

Previous and next or Horse's mouth home

Forward to Basic OO principles

Balloon Journey in Wiltshire
Melksham in pictures
Application design in PHP - multiple step processes
Basic OO principles
PHP4 v PHP5 - Object Model Difference
Designing a heirarcy of classes - getting inheritance right
In honour of the photograph, I present ... a walk from Reybridge to Lacock
Watching the tele