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).

例 10.41. 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.