scripts with classes will certainly aid you in writing code that can be reused. This is a
good idea, especially if you wish to share your code.
The idea of objects is one of those mind-blowing concepts in computer science. It's hard
to grasp at first, but I can attest that once you get it, it becomes quite natural to think in its
terms. Never the less, you can ignore objects if you wish and return to this chapter later.
Some built-in functions return objects. You can find alternatives that don't, or you can
cast the objects as arrays, as described at the end of this chapter.
Defining a Class
When you declare a class, you are really making a template for the creation of objects.
You list all the variables the object should have and all the functions it will need.
Sometimes these are called properties and methods, respectively. Figure 6-1 displays the
form of a class declaration. Note that inside the curly braces you can only declare
variables with the var statement or declare functions. Listing 6.1 shows the definition of
a class with three properties and two methods.
Figure 6-1. Defining a class.When you declare a property, you don't specify a data type. It is a variable like any other,
and it may contain an integer, a string, or even another object. Depending on the
situation, it might be a good idea to add a comment near the declaration of the property
that states its intended use and data type. When you declare a method, you do so just as
you would a function outside a class definition. Both methods and properties exist within
their own scope, or name space. That means you can safely create methods that have the
same name as functions declared outside of class definitions without conflicts. An
exception to this are built-in functions. For example, you cannot have a print method.
Aside from the variables passed as arguments, methods contain a special variable called
this. It stands for the particular instance of the class. You must use this to refer to
properties and other methods of the object. Some object-oriented languages assume an
unqualified variable that refers to a local property, but in PHP any variables referred to
within a method are simply variables local to that scope. Note the use of the this
variable in the constructor for the user class in Listing 6.1.
If you choose to declare a function within a class that has the same name as the class
itself, the function will be considered a constructor and will be executed immediately
upon creating an object from that class. Typically the constructor is used to initialize the
object's properties. Like any other function, the constructor may have parameters and