Page 225 - Beginning PHP 5.3

Chapter 8: Objects
To test these methods, the script then creates a new Car object, $myCar , and sets five properties. The
first three are actual properties in the Car class — $manufacturer , $model , and $color — so these
properties get set to “Volkswagen” , “Beetle” , and “red” . The fourth property, $engineSize ,
doesn ’ t exist in the class, so the __set() method is called; this in turn creates an array element in
$_extraData with a key of “engineSize” and a value of 1.8 .

Similarly, the fifth property, $otherColors , also doesn ’ t exist in the Car class, so __set() is called,
creating an array element in $extraData with a key of “otherColors” that stores the passed - in
value, which in this case is an array containing the strings “green” , “blue” , and “purple”.

Next, the script displays the values of some of the properties of the $myCar object. Notice that, to the
calling code, the $engineSize property is as “ real ” as the $manufacturer property, even though
the $engineSize property doesn ’ t exist in the Car class. The script also tries to retrieve the value of a
property called $fuelType ; because this doesn ’ t exist in the class or in the $_extraData array, the __get()
method returns null to the calling code. This is why no value is displayed in the page.
Finally, the script dumps the contents of the $myCar object using print_r() . Notice that the extra

“ properties ” — $engineSize and $otherColors — are stored inside the private $_extraData array.
(You can see that print_r() also displays private properties inside an object, which is useful for
debugging.)
Although the nonexistent properties were stored in a private array in this example, they could just as
easily have been stored in a file or database table, or passed via an API (application programming
interface) to another application. This gives you some idea of the power of __get() and __set() .

Overloading Method Calls with __call()

Just as you can use __get() and __set() to handle reading and writing nonexistent properties, you can
also use __call() to handle calls to nonexistent methods of a class. Just create a method named __call()
in your class that accepts the nonexistent method name as a string, and any arguments passed
to the nonexistent method as an array. The method should then return a value (if any) back to the
calling code:

public function __call( $methodName, $arguments ) {
// (do stuff here)
return $returnVal;
}
__call() is very useful if you want to create a “ wrapper ” class that doesn ’ t contain much functionality
of its own, but instead hands off method calls to external functions or APIs for processing.

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