Type Hinting

PHP 5 introduces Type Hinting. Functions are now able to force parameters to be objects by specifying the name of the class in the function prototype.

Example 19-42. Type Hinting example

<?php
// An example class
class MyClass
{
    
/**
     * A test function
     *
     * First parameter must be an object of type OtherClass
     */
    
public function test(OtherClass $otherclass) {
        echo
$otherclass->var;
    }
}

// Another example class
class OtherClass {
    
public $var = 'Hello World';
}
?>

Failing to satisfy the type hint results in a fatal error.

<?php
// An instance of each class
$myclass = new MyClass;
$otherclass = new OtherClass;

// Fatal Error: Argument 1 must be an object of class OtherClass
$myclass->test('hello');

// Fatal Error: Argument 1 must be an instance of OtherClass
$foo = new stdClass;
$myclass->test($foo);

// Fatal Error: Argument 1 must not be null
$myclass->test(null);

// Works: Prints Hello World
$myclass->test($otherclass);
?>

Type hinting also works with functions:

<?php
// An example class
class MyClass {
    
public $var = 'Hello World';
}

/**
* A test function
*
* First parameter must be an object of type MyClass
*/
function MyFunction (MyClass $foo) {
    echo
$foo->var;
}

// Works
$myclass = new MyClass;
MyFunction($myclass);
?>

Type Hints can only be of the object type. Traditional type hinting with int and string are not supported.