PHP: Type Hinting

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). However, if NULL is used as the default parameter value, it will be allowed as an argument for any later call.

Example #1 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 catchable 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 hinting allowing NULL value:


<?php



/* Accepting NULL value */

function test(stdClass $obj = NULL) {



}



test(NULL);

test(new stdClass);



?>

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.