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) or arrays (since PHP 5.1).

Example 19-41. Type Hinting examples


<?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 test function
     *
     * First parameter must be an array
     */
    public function test_array(array $input_array) {
        print_r($input_array);
    }
}

// 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);

// Fatal Error: Argument 1 must be an array
$myclass->test_array('a string');

// Works: Prints the array
$myclass->test_array(array('a', 'b', 'c'));
?>

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 and array (since PHP 5.1) type. Traditional type hinting with int and string isn't supported.