Pro PHP- Patterns, Frameworks, Testing and More

CHAPTER 2 ■ STATIC VARIABLES, MEMBERS, AND METHODS^13

}

$instance1 = new MyObject();

$instance1->myMethod();

$instance2 = new MyObject();

$instance2->myMethod();

Executing Listing 2-2 produces the following output:

2

4

This is the result because the static member variable is shared among all instances of the

class.

Notice the use of the :: scope resolution operator and the self scope instead of $this. This

is because $this refers only to the current instance of the class, whereas self:: refers to the

class itself. Let’s take a closer look at this scope resolution operator.

■Note Unlike with $this, when using static variables, you must include the $ symbol after the scope

resolution operator.

Paamayim Nekudotayim

Say what? OK, I know, paamayim nekudotayim is even hard to read. It literally means “double

colon” in Hebrew. The good news is that you can forget the name right now.

The paamayim nekudotayim symbol, also known as the scope resolution operator, is specified

by a double colon (::) and is used to access different scope levels within classes. This operator

takes a scope on the left and a member on the right.

You can use two magic scopes with the scope resolution operator: self and parent. Addi-

tionally, PHP 6 introduces static scope.

The code shown earlier in Listing 2-2 illustrates access to the self scope. This scope refers

to the current class, but unlike $this, it does not refer to a specific instance of a class. It cannot

be used outside a class and is not knowledgeable of its position in an inheritance tree. That

said, self, when declared in an extended class, can call methods declared in a base class but

will always call the overridden method. This is demonstrated in Listing 2-3.

Listing 2-3. Accessing Functions in a Parent Class with self Scope

class MyObject {

function myBaseMethod() {

echo "I am declared in MyObject\n";

}

}

McArthur_819-9C02.fm Page 13 Friday, February 1, 2008 10:23 AM