Оператор проверки принадлежности к классу

Оператор instanceof используется для определения того, является ли текущий объект экземпляром указанного класса .

Оператор instanceof был добавлен в PHP 5. До этого использовалась конструкция is_a(), которая на данный момент не рекомендуется к применению, более предпочтительно использовать оператор instanceof . 

<?php
class A { }
class B { }

$thing = new A;

if ($thing instanceof A) {
    echo 'A';
}
if ($thing instanceof B) {
    echo 'B';
}
?>

Поскольку объект $thing является экземпляром класса A, и никак не B, то будет выполнен только первый, опирающийся на класс A, блок: 

A

Ознакомьтесь также с описанием функций get_class() и is_a().



Оператор проверки принадлежности к классу
MikeH
10-Mar-2006 03:14
This will fail:

<?
if ($moo instanceof "Moo") echo "Goo\n";
?>

and this will not:

<?
if ($moo instanceof Moo) echo "Goo\n";
?>

and although you cant use a quoted string as the class name to check, you can use a variable like this:

<?
$moo_class = "Moo";
if ($moo instanceof $moo_class) echo "Goo\n";
?>

so if you want to loop through an array of class names to check an object against, you can do it easily.
arnold at bean-it dot nl
24-Feb-2006 03:28
Note that operator 'instanceof' will trigger the autoloader.
If the class does not exists, it is not possible that the object  is an instance of this class (as shown by glen at arkadia-systems dot com). Loading this class will probably be a waste of excecution time, so use class_exists with $autoload set to false before using instanceof.

<?php
   function __autoload($classname)
   {
       if (($fp = @fopen("$classname.php", 'r', 1)) and fclose($fp)) include_once "$classname.php";
   }

   function foo($obj)
   {
       if (class_exists('ABC', false) && $obj instanceof ABC) echo "object is an ABC";
   }
?>
Colin
05-Dec-2005 11:20
To MooGoo:

This will fail, as you pointed out:

<?
if ($moo instanceof "Moo") echo "Goo\n";
?>

but this will not

<?
if ($moo instanceof Moo) echo "Goo\n";
?>

This later example (no quotes around Moo) is shown twice in the example code.
klaazvaag . gmail . com
03-Oct-2005 02:02
If you wish to do a short but dynamic comparison using instanceof, you can use this code:

<?php
class any
{
  function __construct($obj)
  {
   if (is_object($obj))
     if ($obj instanceof self)
       echo '$obj is an instance of '.__CLASS__;
  }
}
?>
MooGoo
01-Sep-2005 07:42
instanceof can compare a class instance to a string which contains a class name. However that string must be contained in a variable, it will not work as a return value from a function (for instance, get_class()) or even from a regular inline string.

<?php
class Moo
{
   function Goo()
   {
       $moo = "I do nothing";
   }
}

$moo = new Moo;

//Will fail
if ($moo instanceof "Moo") echo "Goo\n";

//Will also fail
if ($moo instanceof get_class($moo)) echo "Goo\n";

//However...

//Will succeed
$className = get_class($moo);

if ($moo instanceof $className) echo "Goo\n";

//Will also succeed
$className = "Moo";

if ($moo instanceof $className) echo "Goo\n";

?>
archanglmr at yahoo dot com
17-Feb-2005 06:37
Negated instanceof doesn't seem to be documented. When I read instanceof I think of it as a compairson operator (which I suppose it's not).

<?php
class A {}
class X {}

//parse error from !
if (new X !instanceof A) {
   throw new Exception('X is not an A');
}
//proper way to negate instanceof ?
if (!(new X instanceof A)) {
   throw new Exception('X is not an A');
}
?>
d dot schneider at 24you dot de
18-Dec-2004 12:42
use this for cross-version development...

<?php

function is_instance_of($IIO_INSTANCE, $IIO_CLASS){
   if(floor(phpversion()) > 4){
       if($IIO_INSTANCE instanceof $IIO_CLASS){
           return true;
           }
       else{
           return false;
           }
       }
   elseif(floor(phpversion()) > 3){
       return is_a($IIO_INSTANCE, $IIO_CLASS);
       }
   else{
       return false;
       }
   }

?>
glen at arkadia-systems dot com
10-Sep-2004 10:00
If you are updating code to replace 'is_a()' with the PHP5 compliant
'instanceof' operator, you may find it necessary to change the basic
architecture of your code to make this work.

'instanceof' will throw a fatal error if the object being checked for does not
exist.

'is_a()' will simply return false under this condition.

In the example below, 'is_a()' would effectively detect the need to create an
instance of class 'A', but in this case 'instanceof' will crash your program
with a fatal error.

<?php
// define classes

// Commenting this class will cause an error when 'instanceof' looks for 'A'
// class A {}

class B {}

// create a new object
// $thing = new A();
$thing = new B();

if (is_a($thing, 'A')) {
   echo 'Yes, $thing is_a A<br>';
} else {
   echo 'No, $thing is not is_a A<br>';
}

if ($thing instanceof A) {
   echo 'Yes, $thing is an instaceof A<br>';
} else {
   echo 'No, $thing is not an instaceof A<br>';
}

?>

>>> Output:
No, $thing is not is_a A
Fatal error: Class 'A' not found in is_a-instanceof.php on line 19
>>>

A suitable work-around for this situation is to check for the existence of the
class before performing the 'instanceof' comparison:

<?php

/* ... */

if (class_exists('A') && $thing instanceof A) {
   echo 'Yes, $thing is an instaceof A<br>';
} else {
   echo 'No, $thing is not an instaceof A<br>';
}

?>
zimba dot spam at gmail dot com
10-Sep-2004 12:17
instanceof cannot use a string for the comparison like is_a.
Instead, you can use a class instance (not documented)
Example :
<?
$x = new myClass();
$y = new myClass();

echo is_a($x, get_class($y));  // Returns true/1

echo $x instanceof get_class($y);  // Doesn't work, instead use :

echo $x instanceof $y;
?>

Cheers,
zimba
"Leo Pedretti" <lpedretti at suserver dot com>
24-Aug-2004 08:59
The instanceof operator also checks the interface tree. For example, the following code:

<?

interface Human {
   public function say($var);
   public function gender();
}

class man implements Human {
   public function say($var) {
   "Oh yeah, $var\n"
   }

   public function gender() {
   return "male";
   }
}

class woman implements Human {
   public function say($var) {
   "Oh dear, $var\n"
   }

   public function gender() {
   return "female";
   }
}

$m = new man;
$w = new woman;
if ($p instanceof Human) {
   print "\$p is Human.\n";
} else {
   print "\$p is not Human.\n";
}
print "\$m is of gender ".$m->gender()."\n";

if ($w instanceof Human) {
   print "\$w is Human.\n";
} else {
   print "\$w is not Human.\n";
}
print "\$w is of gender ".$w->gender()."\n";
?>

Will produce the output

$m is Human.
$m is of gender male
$w is Human.
$w is of gender female
Jesse Scott (scotje at wwc dot edu)
06-Jul-2004 06:52
Since it's not stated authoritatively here, I'll add that instanceof *does* check all the way up the inheritence tree.

So in this code:

<?php
   class A
   {
       var $someProp;
   }
  
   class B extends A
   {
       function showProp()
       {
           echo $someProp;
       }
   }
  
   $obj1 = new B;

   if ($obj1 instanceof A)
       echo "Instanceof checks inheritence tree!";
   else
       echo "Instanceof does not check inheritence tree!";
?>

The first branch of the if/else block is executed since ($obj1 instanceof A) evaulates to TRUE.

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 Last updated: Mon, 14 Nov 2005