类型约束

PHP 5 可以使用类型约束。函数的参数可以指定必须为对象（在函数原型里面指定类的名字），接口，数组（PHP 5.1 起）或者 callable（PHP 5.4 起）。不过如果使用 NULL 作为参数的默认值，那么在调用函数的时候依然可以使用 NULL 作为实参。

如果一个类或接口指定了类型约束，则其所有的子类或实现也都如此。

类型约束不能用于标量类型如 int 或 string。Traits 也不允许。

Example #1 类型约束示例

<?php
//如下面的类
class MyClass
{
    /**
     * 测试函数
     * 第一个参数必须为 OtherClass 类的一个对象
     */
    public function test(OtherClass $otherclass) {
        echo $otherclass->var;
    }


    /**
     * 另一个测试函数
     * 第一个参数必须为数组 
     */
    public function test_array(array $input_array) {
        print_r($input_array);
    }
}

    /**
     * 第一个参数必须为递归类型
     */
    public function test_interface(Traversable $iterator) {
        echo get_class($iterator);
    }
    
    /**
     * 第一个参数必须为回调类型
     */
    public function test_callable(callable $callback, $data) {
        call_user_func($callback, $data);
    }
}

// OtherClass 类定义
class OtherClass {
    public $var = 'Hello World';
}
?>

函数调用的参数与定义的参数类型不一致时，会抛出一个可捕获的致命错误。

<?php
// 两个类的对象
$myclass = new MyClass;
$otherclass = new OtherClass;

// 致命错误：第一个参数必须是 OtherClass 类的一个对象
$myclass->test('hello');

// 致命错误：第一个参数必须为 OtherClass 类的一个实例
$foo = new stdClass;
$myclass->test($foo);

// 致命错误：第一个参数不能为 null
$myclass->test(null);

// 正确：输出 Hello World 
$myclass->test($otherclass);

// 致命错误：第一个参数必须为数组
$myclass->test_array('a string');

// 正确：输出数组
$myclass->test_array(array('a', 'b', 'c'));

// 正确：输出 ArrayObject
$myclass->test_interface(new ArrayObject(array()));

// 正确：输出 int(1)
$myclass->test_callable('var_dump', 1);
?>

类型约束不只是用在类的成员函数里，也能使用在函数里：

<?php
// 如下面的类
class MyClass {
    public $var = 'Hello World';
}

/**
 * 测试函数
 * 第一个参数必须是 MyClass 类的一个对象
 */
function MyFunction (MyClass $foo) {
    echo $foo->var;
}

// 正确
$myclass = new MyClass;
MyFunction($myclass);
?>

类型约束允许 NULL 值：

<?php

/* 接受 NULL 值 */
function test(stdClass $obj = NULL) {

}

test(NULL);
test(new stdClass);

?>

User Contributed Notes

ASchmidt at Anamera dot net 15-Jul-2019 11:20
Sometimes you want to work with classes (not their instances), but Typehinting is only permitted for an object (instance).

Here is sample code that tests whether the parameter is a valid type (the class/subclass/instance of an expected class):

<?php
declare(strict_types=1);

class MyClass {};

function myfunc( $class ) {
    // Validate classname.
    if ( $class instanceof MyClass ) {
        $class = get_class( $class );
    } elseif ( !class_exists( $class ) or !is_a( $class, MyClass::class, true ) ) {
        throw new \TypeError( "$class is not of type " . MyClass::class );  
    }
    // Proceed with processing of MyClass subclass ...
}
 
$myclass = new MyClass;
myfunc( $myclass );                // valid
myfunc( MyClass::class );        // valid
myfunc( \String::class );          // not of type MyClass.
dr dot mustafa dot darwish at gmail dot com 05-Apr-2018 12:33
This matrix demonstrate passing different variable types with different type hints:
<?php

$array = [10, 10.12, true, '10USD', 'USD'];
function getValue($x, $y)
{
    $typeMap = [
        'integer' => 'int',
        'int' => 'int',
        'float' => 'float',
        'double' => 'float',
        'real' => 'float',
        'string' => 'string',
        'boolean' => 'bool',
        'bool' => 'bool',
    ];
    $yType = $typeMap[gettype($y)];
    $xType = $typeMap[gettype($x)];

    if ($xType == 'string')
        $x = "'$x'";
    elseif ($xType == 'bool')
        $x = $x ? 'true' : 'false';
    try {
        eval("if (!function_exists('test$yType')) {function test$yType($yType \$arg){}} test$yType($x);");
    } catch (Error $e) {
        return get_class($e).': '.$e->getMessage();
    }
    return 'Pass';
}

?>
<table border="1" width="50%">
    <thead>

    <tr>
        <td></td>
        <td align="center" colspan="<?= count($array) ?>"><strong>Input value</strong></td>
    </tr>
    <tr>
        <td></td>
        <?php foreach ($array as $header): ?>
            <td><?= gettype($header), ' ', var_export($header) ?></td>
        <?php endforeach; ?>
    </tr>
    </thead>
    <tbody>
    <tr></tr>
    <?php foreach ($array as $y): ?>
        <tr>
            <td><?= gettype($y), ' ', var_export($y) ?></td>
            <?php foreach ($array as $x): ?>
                <td><?= getValue($x, $y); ?></td>
            <?php endforeach; ?>
        </tr>
    <?php endforeach; ?>
    </tbody>
</table>
dr dot mustafa dot darwish at gmail dot com 05-Apr-2018 10:46
the following code demonstrate php7 response to various combination of inputs and type hinting in a simple matrix:
<?php
$array = [10, 10.12, true, '10USD', 'USD'];
function getValue($x, $y)
{
    $typeMap = [
        'integer' => 'int',
        'int' => 'int',
        'float' => 'float',
        'double' => 'float',
        'real' => 'float',
        'string' => 'string',
        'boolean' => 'bool',
        'bool' => 'bool',
    ];
    $yType = $typeMap[gettype($y)];
    $call = 'test($x)';
    if ($yType == 'string')
        $call = 'test(\'$x\')';
    $template = <<<TEMPLATE_FUNCTION
  if (!function_exists('test')) {function test($yType \$arg){}}
try{
 $call;
} catch (Error \$e) {
    return \$e->getMessage();
}
return 'Pass';
TEMPLATE_FUNCTION;
    return eval($template);
}

?>
<table border="1" width="50%">
    <thead>

    <tr><td></td><td align="center" colspan="<?= count($array) ?>"><strong>Input value</strong></td></tr>
    <tr>
        <td></td>
        <?php foreach ($array as $header): ?>
            <td><?= gettype($header), ' ', var_export($header) ?></td>
        <?php endforeach; ?>
    </tr>
    </thead>
    <tbody>
    <tr></tr>
    <?php foreach ($array as $y): ?>
        <tr>
            <td><?= gettype($y), ' ', var_export($y) ?></td>
            <?php foreach ($array as $x): ?>
                <td><?= getValue($x, $y); ?></td>
            <?php endforeach; ?>
        </tr>
    <?php endforeach; ?>
    </tbody>
</table>
MiChAeLoKGB 10-Jan-2017 05:23
Please note, that with PHP 7, type hinting is faster than normal implementation.
This has to do with type hinting before PHP 7 allowing only objects and arrays and anything else (scalars) would throw an error.

I did some using code "doom at doom dot pl" posted 2 years ago

Here are results from couple of test runs using PHP 7 (200.000 loops)
- teststringNormal took: 0.01799488067627
- teststringOverhead took: 0.012195825576782

- teststringNormal took: 0.027030944824219
- teststringOverhead took: 0.012197017669678

- teststringNormal took: 0.017856121063232
- teststringOverhead took: 0.012274980545044

As you can see, the overhead is faster and much more consistent.

Here is one run with the is_string check removed from Normal:
- teststringNormal took: 0.010342836380005
- teststringOverhead took: 0.012849092483521
mrice at rcs dot us 19-Apr-2016 01:31
In regards to http://php.net/manual/en/language.oop5.typehinting.php#103729 , when using PHP in Eclipse, the best way to typehint is already available in Eclipse natively.

The format is /* @var $variable ObjectName */

The single /* is important. You can also use namespaces, IE

/* @var $variable \Some\Namespace */

In short, there is no reason to create functions that return itself.
Anonymous 30-Aug-2015 01:52
i think this is pretty close.

$lines=hhb_mustbe('array',file("foofile"));
//either file succeeds, and returns an array, or file returns FALSE which is not an array, which throws an unexpectedValueException.

$socket=hhb_mustbe('Socket',socket_create(AF_INET,SOCK_STREAM,getprotobyname('tcp')));
//either socket_create succeeds, and returns a Socket, or socket_create returns False, which is not a resource of type Socket, and you get an UnexpectedValueException

$size=hhb_mustbe('int',filesize(somefile));
//either filesize() returns an integer, or returns FALSE wich is not an int, and you'll get UnexpectedValueException.

    function hhb_mustbe(/*string*/$type,/*mixed*/$variable){
        //should it be UnexpectedValueException or InvalidArgumentException?
        //going with UnexpectedValueException for now...
        $actual_type=gettype($variable);
        if($actual_type==='unknown type'){
            //i dont know how this can happen, but it is documented as a possible return value of gettype...
            throw new Exception('could not determine the type of the variable!');
        }
        if($actual_type==='object'){
            if(!is_a($variable,$type)){
                $dbg=get_class($variable);
                throw new UnexpectedValueException('variable is an object which does NOT implement class: '.$type.'. it is of class: '.$dbg);
            }
            return $variable;
        }
        if($actual_type==='resource'){
            $dbg=get_resource_type($variable);
            if($dbg!==$type){
                throw new UnexpectedValueException('variable is a resource, which is NOT of type: '.$type.'. it is of type: '.$dbg);
            }
            return $variable;
        }
        //now a few special cases
        if($type==='bool'){
            $parsed_type='boolean';   
            } else if($type==='int'){
            $parsed_type='integer';
            } else if($type==='float'){
            $parsed_type='double';
            } else if($type==='null'){
            $parsed_type='NULL';
            } else{
            $parsed_type=$type;
        }
        if($parsed_type!==$actual_type && $type!==$actual_type){
            throw new UnexpectedValueException('variable is NOT of type: '.$type.'. it is of type: '.$actual_type);
        }
        //ok, variable passed all tests.
        return $variable;
    }
doom at doom dot pl 06-Mar-2014 09:16
I've done some tests of the overhead that class Typehint  gives us.
At my PC it goes as follows:
teststringNormal took: 0.041965961456299
teststringOverhead took: 0.48374915122986
It's like 10x longer time (not mention about memory usage), it's just because exception is thrown EVERY SINGLE TIME, along with expensive preg_match() and debug_backtrace() calls.
I think that using class in bigger applications will increase overhead like 100% or more.
<?php

function teststringOverhead(string $string) {
    return $string;
}
function teststringNormal($string){
    if(!is_string($string)){
        return;
    }
    return $string;
}
$loopTimes = 20000;

/////////// test of overhead implementation vs normal
$t1 = microtime(true);
for($i = 0; $i <= $loopTimes; $i++)  teststringNormal("xxx");
echo "<br>teststringNormal took: " . (microtime(true) - $t1);

$t2 = microtime(true);
for($i = 0; $i <= $loopTimes; $i++)  teststringOverhead("xxx");
echo "<br>teststringOverhead took: " . (microtime(true) - $t2);
?>
sorin dot badea91 at gmail dot com 25-Apr-2013 03:05
I've implemented a basic function to ensure argument's type.

<?php
/**
 * Primary types
 */
class Type
{
    const SKIP     = 0;
    const INT      = 1;
    const STRING   = 2;
    const BOOLEAN  = 3;
    const CALLBACK = 4;
    const FLOAT    = 5;
    const RESOURCE = 6;
}

/**
 * @throws InvalidArgumentException
 */
function ensureType()
{
    $debugStack = debug_backtrace();
    $argv       = $debugStack[1]['args'];
    $types      = func_get_args();
    foreach ($argv as $key => $value) {
        $message = null;
        if (is_null($value)) {
            continue;
        }
        switch ($types[$key]) {
            case Type::INT:
                if (!is_int($value)) {
                    $message = 'Argument ' . $key . ' passed to ' . $debugStack[1]['function'] . '() must be of type int';
                }
                break;
            case Type::STRING:
                if (!is_string($value)) {
                    $message = 'Argument ' . $key . ' passed to ' . $debugStack[1]['function'] . '() must be of type string';
                }
                break;
            case Type::BOOLEAN:
                if (!is_bool($value)) {
                    $message = 'Argument ' . $key . ' passed to ' . $debugStack[1]['function'] . '() must be of type boolean';
                }
                break;
            case Type::CALLBACK:
                if (!is_callable($value)) {
                    $message = 'Argument ' . $key . ' passed to ' . $debugStack[1]['function'] . '() must be a valid callback';
                }
                break;
            case Type::FLOAT:
                if (!is_float($value)) {
                    $message = 'Argument ' . $key . ' passed to ' . $debugStack[1]['function'] . '() must be of type float';
                }
                break;
            case Type::RESOURCE:
                if (!is_resource($value)) {
                    $message = 'Argument ' . $key . ' passed to ' . $debugStack[1]['function'] . '() must be of type resource';
                }
                break;
        }
        if (!is_null($message)) {
            if (is_object($value)) {
                $message .= ', instance of ' . get_class($value) . ' given';
            } else {
                $message .= ', ' . gettype($value) . ' given';
            }
            throw new InvalidArgumentException($message);
        }
    }
}

function dummyFunction($var1, $var2, $var3)
{
    ensureType(Type::BOOLEAN, Type::INT, Type::STRING);
}

$object = new ReflectionClass('ReflectionClass');

dummyFunction(1, $object, 'Hello there');
michaelrfairhurst at gmail dot com 17-Feb-2013 09:46
The scalar type hinting solutions are all overthinking it. I provided the optimized regex version, as well as the fastest implementation I've come up with, which just uses strpos. Then I benchmark both against the TypeHint class.

<?php
function optimized_strpos($ErrLevel, $ErrMessage) {
        if ($ErrLevel == E_RECOVERABLE_ERROR
            // order this according to what your app uses most
            return strpos($ErrMessage, 'must be an instance of string, string')
                || strpos($ErrMessage, 'must be an instance of integer, integer')
                || strpos($ErrMessage, 'must be an instance of float, double')
                || strpos($ErrMessage, 'must be an instance of boolean, boolean')
                || strpos($ErrMessage, 'must be an instance of resource, resource');
}

function optimized_regex($ErrLevel, $ErrMessage) {
        if ($ErrLevel == E_RECOVERABLE_ERROR) {
            if(preg_match('/^Argument \d+ passed to (?:\w+::)?\w+\(\) must be an instance of (\w+), (\w+) given/', $ErrMessage, $matches))
                return $matches[1] == ($matches[2] == 'double' ? 'float' : $matches[2]);
        }
}
?>

BENCHMARKING Typehint::handleTypehint()
string type hint.....[function it(string $var) {}]............2.1588530540466 seconds
float type hint......[function it(float $var) {}].............2.1563150882721 seconds
integer type hint....[function it(integer $var) {}]...........2.1579530239105 seconds
boolean type hint....[function it(boolean $var) {}]...........2.1590459346771 seconds

BENCHMARKING optimized_regex()
string type hint.....[function it(string $var) {}]............0.88872504234314 seconds
float type hint......[function it(float $var) {}].............0.88528990745544 seconds
integer type hint....[function it(integer $var) {}]...........0.89038777351379 seconds
boolean type hint....[function it(boolean $var) {}]...........0.89061188697815 seconds

BENCHMARKING optimized_strpos()
string type hint.....[function it(string $var) {}]............0.52635812759399 seconds
float type hint......[function it(float $var) {}].............0.74228310585022 seconds
integer type hint....[function it(integer $var) {}]...........0.63721108436584 seconds
boolean type hint....[function it(boolean $var) {}]...........0.8429491519928 seconds
john at cast dot com 29-Apr-2011 06:33
i use eclipse ganymede as an IDE and it offers "intellisense" where it can, i.e. when variables are "declared" via type hinting or a "new"-statement . i found using the following pattern helps eclipse along as well:

<?php
class MyClass{

  public static function Cast(MyClass &$object=NULL){
       return $object;
  }

  public method CallMe(){
  }
}

$x=unserialize($someContent);
$x=MyObject::Cast($x);
$x->CallMe();
?>

after calling Cast(), due to the type hinting, eclipse offers me the "CallMe" function in a dropdown when i type "$x->" in the code afterwards.

i found this very practical und included the Cast() function in my code template for new classes. i've been wondering, if there is a drawback i oversaw, but i haven't noticed any negative effects so far... maybe some of you will find this just as handy as i do ;o)

p.s. do note: when used in inherited classes a STRICT-notice comes up, because the function definition of the inherited class doesn't match the parent's definition (different type hinting) - but it works great!
alejosimon at gmail dot com 22-Oct-2010 11:55
For PHP 5.3 version and namespaces support.

<?php

function phpErrorHandler( $code, $message, $file, $line ) {

    if ( error_reporting() & $code ) {

        if ( $code == E_RECOVERABLE_ERROR ) { // Scalar Type-Hinting patch.

            $regexp = '/^Argument (\d)+ passed to (.+) must be an instance of (?<hint>.+), (?<given>.+) given/i' ;

            if ( preg_match( $regexp, $message, $match ) ) {

                $given = $match[ 'given' ] ;
                $hint  = end( explode( '\\', $match[ 'hint' ] ) ) ; // namespaces support.

                if ( $hint == $given ) return true ;
            }
        }

        return false ;
    }
}

set_error_handler( 'phpErrorHandler' ) ;

/************************************/

function typeHintTest( integer $arg1 ) {

    print_r( $arg1 ) ;
}

typeHintTest( true ) ; // Error throw because not integer type.

?>
gdecad at NOSPAM dot example dot com 22-Oct-2010 06:02
I have made a little bench between three method of type hinting for native type (string, integer, ...).

First method : by test type in function like :
<?php
function testTest($arg) {
    if (!is_string($arg)) {
        trigger_error('Argument $arg passed to test must be an instance of string, other given');
    }
    return $arg;
}
?>

Second method : by object representing native type :
<?php
function testObject(StringObj $arg) {
    return $arg;
}
?>

Third method : by class TypeHint proposed by Daniel :
<?php
function testHint(string $arg) {
    return $arg;
}
?>

the results are here :
bench for 100000 iterations,  in seconds
        avg                    min                    max                    total
test    5.3275489807129E-6    2.8610229492188E-6    0.0033020973205566    0.53275895118713
object    4.9089097976685E-6    3.814697265625E-6    0.0025870800018311    0.49089503288269
hint    3.2338891029358E-5    2.9802322387695E-5    0.0025920867919922    3.2338931560516

As you can see, the method by object is the best
now you know...
dpariyskiy at netatwork dot com 08-Sep-2009 08:36
Daniel, thank you for the type hinting class. Very useful.
For anyone having a problem where php isn't setting Daniel's error handler, as was the case for me, try changing initializeHandler function to the following:

<?php
public static function initializeHandler()
{
   
    set_error_handler(array('Typehint','handleTypehint'));
   
    return TRUE;
}
?>

Hope this helps,
--Dmitriy
bantam at banime dot com 06-Jan-2009 02:53
Daniel's typehint implementation was just what I was looking for but performance in production wasn't going to cut it. Calling a backtrace every time hurts performance. For my implementation I didn't use it, after all, PHP tells us what the data type is in the error message, I don't feel I need to evaluate the argument where I am using typehinting. Here is the cut down version I use in my error handling class:

<?php
        public static function typehint($level, $message)
        {
            if($level == E_RECOVERABLE_ERROR)
            {
                if(preg_match('/^Argument (\d)+ passed to (?:(\w+)::)?(\w+)\(\) must be an instance of (\w+), (\w+) given/', $message, $match))
                {
                    if($match[4] == $match[5])
                        return true;
                }
            }
           
            return false;
        }
?>

Hope this can be of use to somebody.
wickedmuso at gmail dot com 24-Oct-2008 08:26
One useful thing with Type Hinting that I could not find in the documentation (but tested) is that you can also use an Interface in the hint (versus a Class).  This is a very useful tool if you are trying to code to Interfaces rather than Classes (which is common in Test Driven Development and Dependency Injection paradigms).  It means your external class can present itself into the method as long as it implements the nominated Interface (obviously).
info at thewebsiteguy dot com dot au 08-Oct-2008 06:30
I find it rather frustrating that PHP has internal data types but doesn't allow optional hinting for it.  I REALLY needed it for something, so I found a way around it.

<?php
abstract class DataType
{
    protected $length;
    protected $precision;
    protected $number;
   
  public function __construct()
  {
    $this->number = false;
    $this->precision = null;
  }
   
    public function GetLength()
    {
        return $this->length;
    }
   
    public function IsNumber()
    {
        return $this->number;
    }

    public function GetPrecision()
    {
        return $this->precision;
    }
}

class Integer extends DataType
{
    public function __construct($length = 12)
    {
        parent::__construct();
        $this->number = true;
        $this->length = $length;
        $this->precision = 0;
    }
}

class Float extends DataType
{
  public function __construct($length = 12, $precision = 2)
  {
    parent::__construct();
    $this->number = true;
    $this->length = $length;
    $this->precision = $precision;
  }
}

class String extends DataType
{
    public function __construct($length = 255)
    {
        parent::__constructor();
        $this->length = $length;
    }
}
//etc etc through the types...
?>

then later I can do this...

<?php
final class Field
{
    public $Name;
    public $Mandatory;
    public $Hidden;
    public $ListField;
    public $Value;
    public $ForeignClass;
    public $ReadOnly;
    public $DataType;
   
    public function __construct($name, DataType $dataType, $mandatory = false, $listField = true, $value = null, $readOnly = false, BaseCBO $foreignClass = null)
    {
        $this->Name = $name;
        $this->DataType = $dataType;
        $this->Mandatory = $mandatory;
        $this->ListField = $listField;
        $this->Value = $value;
        $this->ReadOnly = $readOnly;
        $this->ForeignClass = $foreignClass;
    }
}

// ....

class DoSomeStuff
{
    public function DoGenericThings(Field $field)
    {
        if ($field->DataType instanceof Integer)
        {
            // do things for an integer field...
        }
    }
}
?>
wbcarts at juno dot com 01-Oct-2008 06:20
TYPE-HINTING and VISIBILITY

Type-hinting is just one more small piece of PHP that protects our objects when visibility cannot.

<?php

class Point {
  public $x, $y;

  public function __construct($xVal = 0, $yVal = 0) {
    $this->x = $xVal;
    $this->y = $yVal;
  }
}

class Polyline {
  protected $points = array();

  public function addPoint(Point $p) {  // the line we're interested in...
    $this->points[] = $p;
  }
}

$point1 = new Point(15, 12);
$polyline = new Polyline();
$polyline->addPoint($point1);
$polyline->addPoint(new Point(55, 22));
$polyline->addPoint(new Point(33, 31));

$polyline->addPoint(new stdClass());    // PHP will throw an error for us! 

?>

Since our Polyline::addPoint() function has to be public, any outside code can try to pass anything. But, when type-hinting is declared, PHP throws an error when phoney data tries to sneak by.
DanielLWood [at] Gmail [dot] Com 08-Sep-2008 05:59
To follow up on my original post dealing with the type hinting class I provided:

Kalkamar is absolutely correct, it is slow and is a hack.  Everyone who uses it and wants to see this type of syntax native needs to post on the 'php internals' development thread in support.

Thanks,

Dan
kalkamar at web dot de 04-Sep-2008 02:24
I really like the Daniel`s Typehinting-Class, but you please not that it may be relevant for the performance if you use Typehinting for scalar values very often.

Here is my performance-test:

<?php

function notypehinting($x)
{
    is_string($x);   //checking the type manually instead
}

function typehinting(string $x)
{
}

$test=new timer;
for($i=0;$i<10000;$i++)
{
try{
    notypehinting('test');
}
catch(Exception $e){}
}
echo $test.'<br>';

$test2=new timer;
for($i=0;$i<10000;$i++)
{
try{
    typehinting('test');
}
catch(Exception $e){}
}
echo $test2.'<br>';
?>

Output:

0.0088460445404053
0.21634602546692

Result:
typehinting() ist more than 20 times slower than notypehinting()

You see: typehinting for scalar types (like suggested by Daniel) is not the best thing for the performance if you use it very often.
marcus at ignorethis netweblogic dot com 14-Jul-2008 06:18
Love the typehint object Daniel. Great effort!

However, it still throws catchable fatal errors, which is not what I want, so I added one line to handleTypehint() so it throws an Exception.

<?php
public static function handleTypehint($ErrLevel, $ErrMessage) {
        if ($ErrLevel == E_RECOVERABLE_ERROR) {
            if (preg_match ( TYPEHINT_PCRE, $ErrMessage, $ErrMatches )) {
                list ( $ErrMatch, $ThArgIndex, $ThClass, $ThFunction, $ThHint, $ThType ) = $ErrMatches;
                if (isset ( self::$Typehints [$ThHint] )) {
                    $ThBacktrace = debug_backtrace ();
                    $ThArgValue = NULL;
                    if (self::getTypehintedArgument ( $ThBacktrace, $ThFunction, $ThArgIndex, $ThArgValue )) {
                        if (call_user_func ( self::$Typehints [$ThHint], $ThArgValue )) {
                            return TRUE;
                        }
                    }
                }
                throw new Exception($ErrMessage);
            }
        }
        return FALSE;
    }
?>
Daniel dot L dot Wood at Gmail dot Com 26-May-2008 11:00
People often ask about scalar/basic typehints.  Here is a drop in class that I use in my MVC framework that will enable typehints through the use of a custom error handler.

Note: You should include this code above all other code in your include headers and if you are the using set_error_handler() function you should be aware that this uses it as well.  You may need to chain your set_error_handlers()

Why?
1) Because people are sick of using the is_* functions to validate parameters.
2) Reduction of redundant coding for defensive coders.
3) Functions/Methods are self defining/documenting as to required input.

Also..
Follow the discussion for typehints in PHP 6.0 on the PHP Internals boards.

<?php

define('TYPEHINT_PCRE'              ,'/^Argument (\d)+ passed to (?:(\w+)::)?(\w+)\(\) must be an instance of (\w+), (\w+) given/');

class Typehint
{

    private static $Typehints = array(
        'boolean'   => 'is_bool',
        'integer'   => 'is_int',
        'float'     => 'is_float',
        'string'    => 'is_string',
        'resrouce'  => 'is_resource'
    );

    private function __Constrct() {}

    public static function initializeHandler()
    {

        set_error_handler('Typehint::handleTypehint');

        return TRUE;
    }

    private static function getTypehintedArgument($ThBackTrace, $ThFunction, $ThArgIndex, &$ThArgValue)
    {

        foreach ($ThBackTrace as $ThTrace)
        {

            // Match the function; Note we could do more defensive error checking.
            if (isset($ThTrace['function']) && $ThTrace['function'] == $ThFunction)
            {

                $ThArgValue = $ThTrace['args'][$ThArgIndex - 1];

                return TRUE;
            }
        }

        return FALSE;
    }

    public static function handleTypehint($ErrLevel, $ErrMessage)
    {

        if ($ErrLevel == E_RECOVERABLE_ERROR)
        {

            if (preg_match(TYPEHINT_PCRE, $ErrMessage, $ErrMatches))
            {

                list($ErrMatch, $ThArgIndex, $ThClass, $ThFunction, $ThHint, $ThType) = $ErrMatches;

                if (isset(self::$Typehints[$ThHint]))
                {

                    $ThBacktrace = debug_backtrace();
                    $ThArgValue  = NULL;

                    if (self::getTypehintedArgument($ThBacktrace, $ThFunction, $ThArgIndex, $ThArgValue))
                    {

                        if (call_user_func(self::$Typehints[$ThHint], $ThArgValue))
                        {

                            return TRUE;
                        }
                    }
                }
            }
        }

        return FALSE;
    }
}

Typehint::initializeHandler();

?>

An are some examples of the class in use:

<?php

function teststring(string $string) { echo $string; }
function testinteger(integer $integer) { echo $integer; }
function testfloat(float $float) { echo $float; }

// This will work for class methods as well.

?>

You get the picture..
jesdisciple @t gmail -dot- com 06-Nov-2007 07:50
The manual's sample code says:
<?php
//...
// Fatal Error: Argument 1 must not be null
$myclass->test(null);
//...
?>

And this is true, unless a default value of NULL is given; in fact, this is the only way to give a default value for object arguments (as a default value must be a constant expression):
<?php
$mine = new MyClass();
$mine->test(NULL);
class MyClass{
    public function __construct(OtherClass $arg = NULL){
        if(is_null($arg)){
            //Apply default value here.
        }
    }
    public function test(array $arr = NULL){
        print_r($arr);
    }
}
class OtherClass{
   
}
?>
mlovett at morpace dot com 06-Jul-2005 03:54
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.