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).

例子 19-39. 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.

add a note User Contributed Notes

mega-squall at caramail dot com
16-May-2006 03:11


Type hinting cannot be used with array of instances of a given class. When submited to PHP Team, idea got this answer :



" That's impossible and never will be. But you can do that more or less yourself. Derive a class that implements ArrayAccess or reuse ArrayObject/ArrayIterator. And overload its offsetSet(). In the method body you add the check to ensure only what you want can go in. Now if that class accepts only B's (B beeing an examble classname, ndla) you may call it ArrayOfB and the use ArrayOfB as you typehint. "



This is obviously reaching the limit between "typing" and "type hinting" ...

mlovett at morpace dot com
06-Jul-2005 06:54


Type hinting works with interfaces too. In other words, you can specify the name of an interface for a function parameter, and the object passed in must implement that interface, or else type hinting throws an exception.

caliban at darklock dot com
23-Feb-2005 11:34


In case you're worried, type hinting does allow descendants. Extending the documentation example:



<?php

   // Example class

   class MyClass

   {

      public function test(OtherClass $otherclass) 

      {

          if(is_callable(array($otherclass,$otherclass->var)))

          {

             $otherclass->{$otherclass->var}();

          }

          else

          {

             echo $otherclass->var;

          }

      }

   }



   // Another example class

   class OtherClass 

   {

      public $var = 'Hello World';

   }



   // Yet another example class

   class DerivedClass extends OtherClass 

   {

      function __construct() 

      { 

         $this->var="Planet"; 

      }



      public function Planet()

      {

         echo "Hello ".$this->var;

      }

   }



   $myclass = new MyClass;

   $otherclass = new OtherClass;

   $derivedclass = new DerivedClass;



   // Works - prints "Hello World"

   $myclass->test($otherclass);



   // Works - calls DerivedClass::Planet()

   //    which prints "Hello Planet"

   $myclass->test($derivedclass);

?>

add a note