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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 331202 $ -->
<sect1 xml:id="language.oop5.typehinting" xmlns="http://docbook.org/ns/docbook">
<title>Type Hinting</title>
<para>
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), interfaces, arrays (since PHP 5.1) or <type>callable</type>
(since PHP 5.4). However, if <type>NULL</type> is used
as the default parameter value, it will be allowed as an argument for any
later call.
</para>
<para>
If class or interface is specified as type hint then all its children or
implementations are allowed too.
</para>
<para>
Type hints can not be used with scalar types such as <type>int</type> or
<type>string</type>.
<link linkend="language.types.resource">Resources</link> and <link linkend="language.oop5.traits">Traits</link> are not allowed either.
</para>
<example>
<title>Type Hinting examples</title>
<programlisting role="php">
<![CDATA[
<?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);
}
/**
* First parameter must be iterator
*/
public function test_interface(Traversable $iterator) {
echo get_class($iterator);
}
/**
* First parameter must be callable
*/
public function test_callable(callable $callback, $data) {
call_user_func($callback, $data);
}
}
// Another example class
class OtherClass {
public $var = 'Hello World';
}
?>
]]>
</programlisting>
<para>
Failing to satisfy the type hint results in a catchable fatal error.
</para>
<programlisting role="php">
<![CDATA[
<?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'));
// Works: Prints ArrayObject
$myclass->test_interface(new ArrayObject(array()));
// Works: Prints int(1)
$myclass->test_callable('var_dump', 1);
?>
]]>
</programlisting>
<para>
Type hinting also works with functions:
</para>
<programlisting role="php">
<![CDATA[
<?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);
?>
]]>
</programlisting>
<para>
Type hinting allowing NULL value:
</para>
<programlisting role="php">
<![CDATA[
<?php
/* Accepting NULL value */
function test(stdClass $obj = NULL) {
}
test(NULL);
test(new stdClass);
?>
]]>
</programlisting>
</example>
</sect1>
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