ZEND PHP 5 Certification STUDY GUIDE

118 ” Object Oriented Programming in PHP
Constructors
PHP 5 introduces the concept of the unified constructor and, along with it, a new
destructor for objects. The constructor and destructor are special class methods that
are called, as their names suggest, on object creation and destruction, respectively.
Constructors are useful for initializing an object’s properties, or for performing startup
procedures, such as, for example, connecting to a database, or opening a remote
file.
The concept of the constructor is, of course, not new to PHP 5. In PHP 4, it was
possible to define a class method whose name was the same as the class itself; PHP
would then consider this method to be the class’ constructor and call it whenever
a new instance of the class was created. This approach had several drawbacks—for
example, if you decided to rename your class, you would also have to rename your
constructor.
To avoid these problems, PHP 5 now uses the magic __construct() method as the
constructor for any class regardless of the class’ name. This greatly simplify things,
and provides you with a standard mechanism to recognize and call constructors in a
consistent manner:
class foo {
function __construct()
{
echo __METHOD__;
}
function foo()
{
// PHP 4 style constructor
}
}
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new foo();
This example will display foo::__construct (the __METHOD__ constant is replaced at
compilation time with the name of the current class method). Note that, if the
__construct() method is not found, PHP will look for the old PHP 4-style constructor
(foo) and call that instead.