Introduction

Continuing our PHP functions article, we move on to creating classes. Let me say right at the start that you can write perfectly effective and useful PHP code without creating classes or going into object oriented programming. Another thing is that PHP, at its core, is not an object oriented language. This is because PHP was built from the C language, which is at its core a procedural language, rather than a methodical one. However, object oriented programming can be very powerful and PHP programmers are increasingly taking advantage of these capabilities, which have been greatly expanded since PHP4.

What is a class?

A class is a collection of variables and functions that serves a common purpose. It gives you the ability to think about real world objects and translate them into code. For example, let's try to describe a car. The class "car" might have variables: $name_of_car, $wheels, $steeringwheel, $windscreen, $lights, $pedals and $brakes. The functions of a car might include Turnleft(),Turnright() and Accelerate(). The function "Accelerate()" might take arguments such as $increase_speed. Now, all of the above describes a car and what a car does in both real terms and in code.

Now you might ask, couldn't  this be done with regular functions and variables? Yes, it could, especially if you were talking about one car. But if you are talking about more than one car, then it would be impossible to keep up with all the various variables and functions associated with multiple cars. This is where classes become very useful, because classes bring all those variables and functions under one name. In this case, it's an object named "car." Now if you have more than one car, all you have to do is instantiate that object. The term instantiate basically means making a copy of the object. The new copy will have all the variables and functions of the original object available to it. You can include the class in any script that you create; the class will work the same.

Let me sound a cautionary note. Although OOP makes coding easier and more portable, the objects' execution time is less efficient than writing straight code. And while OOP speeds up project development drastically, more often than not, it produces less customized and slower applications. So, be aware of these pitfalls when choosing to use OOP.

OOP is arguably difficult to learn, so in this article I am going to use very simple examples to demonstrate how to use OOP. This should help new users grasp the concepts easily. Also, because OOP is such a huge topic I will only deal with the basics so as to give you the ability to easily learn the more advanced aspects of it.

A class has the following members:

Attributes

Methods

A good example of a class is Human. A human class would have characteristics (attributes) of gender, hands, legs, age, and so forth. It would also have actions (methods) such as walking, eating, running, talking, and so on.

The syntax of a class is as follows:

class class_name{
var $variable_name;
functionfunction_name(){
statements;
}
}

Notice that within the class you use the var keyword to identify your variables. At this point you can also assign a value to your variables. Try to use the same naming conventions as you would for functions. It is easier to recognize what a class is if it reflects its purpose(e.g. class Human_class{). Another keyword, $this, is used to refer to the instances of an object and its attributes e.g. $this->$variable_name. To instantiate a class means to create a new version of it. Say we  have a class called dog, to instantiate it, we do this:

$rex = new dog();

Now, rex will have all the attributes of the class dog.