On PHPMaster.com there's a new tutorial from Alejandro Gervasio about subtype polymorphism. It sounds a little scary, but really it's just a look at sub-objects that inherit from parents and how to swap them around at runtime to do different things.

In this article I'll show you how to exploit the virtues that Polymorphism offers through the development of a pluggable cache component. The core functionality can be expanded later to suit your needs through the development of additional cache drivers.

He starts off with the definition of an interface to provide structure to the sample application (the CacheInterface) and implements it in two different subtypes - a FileCache and an AppCache (using the file system and APC, respectively). He builds on these and creates a "View" that uses these caching systems to generate and save the output to a cache for use later in the execution.

If you haven't taken much of a look at design patterns and how they can help your development life, the Singleton pattern is a good place to start. On PHPBuilder.com there's a new tutorial introducing this handy pattern and how it might fit your needs.

One of these patterns is the Singleton design pattern, which is based on the mathematical concept of a singleton (a set with a single element). [...] Sometimes the Singleton pattern can help complete important programming tasks, but only you can decide where and when it fits your needs. As a pointer, the Singleton pattern fits well when you manage a shared resource [...] because your application should have only a single instance in order to avoid conflicting requests for the same resource and to minimize performance issues.

He shows an example of how to implement it, first as a class template and then in actual use (complete with code ready to copy and paste). He also shows how you can use the singleton pattern to act as a frontend to other classes, making a sort of polymorphism simple. Thankfully, he also explains some of the risks in using this design pattern and that "less is more".

On the NETTUTS.com site today there's a new tutorial by Steve Guidetti about understanding and handling polymorphism in PHP - making interfaces to multiple objects that all work the same way. In this tutorial he gets more in depth and includes some code to illustrate.

In object oriented programming, polymorphism is a powerful and fundamental tool. It can be used to create a more organic flow in your application. This tutorial will describe the general concept of polymorphism, and how it can easily be deployed in PHP.

He explains to concept of polymorphism for those that haven't seen it before - common interfaces to multiple objects - and how to can help make using the parts of your application much simpler. In his code examples he uses interfaces and abstract classes to make the connections. The interfaces define the structure to follow and the abstract classes are the multiple objects that must follow it.

DevShed has posted the final part of their look at using polymorphism with objects in PHP5, this time with a focus on validating incoming data from a form.

In this final installment of the series I'm going to show you how to develop an expandable PHP mechanism for validating different types of incoming data. This will demonstrate how this important pillar of object-oriented programming can be used with a plethora of applications.

They show how to create a simple DataValidator class to act as a base to build from. On top of this, they create classes to validate if the value is:

• empty
• an integer
• if it's numeric
• if it's in a certain range
• if it's alphanumeric
• if it's alphabetic
• or if it's a valid email address

They also include how to implement these filters, showing a simple Factory pattern that creates the object and runs the value through its validation.

DevShed continues their look at using polymorphism in an application with the latest part of the series - "Building Dynamic Web Pages with Polymorphism in PHP 5".

In short, Polymorphism is a feature exposed by certain objects that belong to the same family, which eventually can behave differently, even when they're using identical methods. Or more clearly, an object can be considered polymorphic when it's capable of performing different actions by utilizing the same method.

This time they focus on web page development that uses this object-oriented practice. The create a WebPageElement that you can ID and class attributes on and use it to create HTML widgets and extend them to create Div and Link element.

In a new article from DevShed, they walk you through a method of using abstraction and objects along with polymorphism to work with databases.

I'll be explaining how to implement Polymorphism to achieve a high level of abstraction when accessing different database systems. Subsequent articles will cover the use of polymorphic objects to build dynamic web documents and validate user-supplied input.

They start out with a bad example of a database link in a PHP script, a database handler that, based on what type of database you tell it you're using, handles the requests appropriately. This is good, but poor design - their alternative is using objects (created from classes of one type for each kind of database). These are pulled together in a factory class and the correct one is built - out into a generic database object that's smart enough to know what it's supposed to do.

DevShed is continuing on with their series looking at advanced concepts of object oriented PHP with this new tutorial. It's part three of four parts, looking this time at polymorphism and design patterns in PHP.

Last week, we continued our discussion of the object-oriented features of PHP 5 by taking a first look at design patterns. This week, we will continue looking at design patterns, and examine polymorphism. This article, the third of four parts, is excerpted from chapter two of the book Advanced PHP Programming, written by George Schlossnagle.

They cover some of the more handy features OOP in PHP5, including interfaces, type hinting, the factory pattern and the singleton pattern.

Nefarious Designs has posted the next part of their "Object-Oriented PHP" series today, the third part looking at how to take the relationships (discussed in part two) even further.

In "Part 1: Definition" we took a look at defining objects and classes in PHP. In "Part 2: Relationships" we looked at linking our objects and classes together. In part 3 I'm going to add to those relationships by looking at visibility, polymorphism and the scope resolution operator.

He starts off with a look at access modifiers (private, public, protected) on both attributes and methods. Next is a look at polymorphism with an example of using a getHTML function in both a base formElement class and the child class of textarea. He then talks about the scope resolution operator (::) and its use in parent/child relationships and in PHP5's scope.

Some concepts of object-oriented design are harder to figure out that others for a budding programmer. Thankfully, there's articles like this one from DevShed to help fill in some of the gaps. Specifically, they focus on inheritance, polymorphism, and serialization in your PHP classes.

If you are working with classes in PHP, you will sooner or later encounter inheritance, polymorphism, and serialization. The ability to use these three will help speed up your code writing. This article covers how to use them, and more.

First off, they look at inheritance and working with child classes before moving on to polymorphism (similar functionality, different objects), calling functions statically, and serializing objects to make passing them around much easier.

From DevShed, there's a more advanced tutorial that might interest PHP developers out there looking for more info on "polymorphism" for their apps.

This article explains what polymorphism is and how it applies to object oriented design in particular. It also explains the pros and cons of polymorphism when working with certain versions of PHP.

They start with a definition on the topic that doesn't seem to help much: "The occurrence of different forms, stages, or types in individual organisms or in organisms of the same species, independent of sexual variations." They do, however, follow that with what it means to programming: "...an interface or base class without regard to an object's concrete class." They also include a simple example (no code, that's later).

With that concept in place, they move to the next step - working with the example to create code that can be used as a reference point. They talk about using a switch to make the script respond differently to different inputs and the lack of "late binding" support in PHP5.