Operadores
The PHP parser generates a parse error on either of the two lines that are commented out here.
Apparently the 'instanceof' construct will take a string variable in the second spot, but it will NOT take a string... lame
class Bar {}
$b = new Bar;
$b_class = "Bar";
var_export($b instanceof Bar); // this is ok
var_export($b instanceof $b_class); // this is ok
//var_export($f instanceof "Bar"); // this is syntactically illegal
//var_export($f instanceof 'Bar'); // this is syntactically illegal
Operadores de tipo
instanceof é usado para determinar se um variável do PHP é uma objeto instânciado de uma certa classe:
Exemplo #1 Usando instanceof com classes
<?php
class MyClass
{
}
class NotMyClass
{
}
$a = new MyClass;
var_dump($a instanceof MyClass);
var_dump($a instanceof NotMyClass);
?>
O exemplo acima irá imprimir:
bool(true) bool(false)
instanceof pode também ser usado para determinar se uma variável é um objeto instânciado de uma classe que herda de uma classe pai:
Exemplo #2 Usando instanceof com herança
<?php
class ParentClass
{
}
class MyClass extends ParentClass
{
}
$a = new MyClass;
var_dump($a instanceof MyClass);
var_dump($a instanceof ParentClass);
?>
O exemplo acima irá imprimir:
bool(true) bool(true)
Para verificar se um objeto não é uma instância de uma classe, o operador lógico not pode ser usado.
Exemplo #3 Usando instanceof para verificar se o objeto não é uma instância da classe
<?php
class MyClass
{
}
$a = new MyClass;
var_dump(!($a instanceof stdClass));
?>
O exemplo acima irá imprimir:
bool(true)
Por fim, instanceof pode também ser usado para determinar se uma variável é um objeto instânciado de uma classe que implementa uma interface:
Exemplo #4 Usando instanceof para classe
<?php
interface MyInterface
{
}
class MyClass implements MyInterface
{
}
$a = new MyClass;
var_dump($a instanceof MyClass);
var_dump($a instanceof MyInterface);
?>
O exemplo acima irá imprimir:
bool(true) bool(true)
Embora instanceof é usualmente usado com um nome de classe literal, ele pode também ser usado com outro objeto ou uma variável string:
Exemplo #5 Usando instanceof com outras variáveis
<?php
interface MyInterface
{
}
class MyClass implements MyInterface
{
}
$a = new MyClass;
$b = new MyClass;
$c = 'MyClass';
$d = 'NotMyClass';
var_dump($a instanceof $b); // $b é umn objeto da classe MyClass
var_dump($a instanceof $c); // $c é uma string 'MyClass'
var_dump($a instanceof $d); // $d é uma string 'NotMyClass'
?>
O exemplo acima irá imprimir:
bool(true) bool(true) bool(false)
Há algumas detalhes para estar ciente. Antes do PHP 5.1.0, instanceof podia chamar __autoload() quando o nome da classe não existe. Em adicional, se a classe não foi carregada, um erro fatal poderia ocorrer. Isto pode funcionar usando a dynamic class reference, ou uma variável string contendo o nome da classe:
Exemplo #6 Evitando que o nome da classe seje verificado e fatal erros com instanceof no PHP 5.0
<?php
$d = 'NotMyClass';
var_dump($a instanceof $d); // não causa erro fatal
?>
O exemplo acima irá imprimir:
bool(false)
O operador instanceof foi introduzido no PHP 5. Antes disso is_a() era usado mas is_a() tornou-se obsoleto pelo instanceof.
Veja também get_class() e is_a().
add a note
User Contributed NotesOperadores de tipo
ejohnson82 at gmail dot com
18-Jan-2008 10:59
18-Jan-2008 10:59
julien plee using g mail dot com
21-Jul-2007 03:56
21-Jul-2007 03:56
Response to vinyanov at poczta dot onet dot pl:
You mentionned "the instanceof operator will not accept a string as its first operand". However, this behavior is absolutely right and therefore, you're misleading the meaning of an instance.
<?php 'ClassA' instanceof 'ClassB'; ?> means "the class named ClassA is an instance of the class named ClassB". This is a nonsense sentence because when you instanciate a class, you ALWAYS obtain an object. Consequently, you only can ask if an object is an instance of a class.
I believe asking if "a ClassA belongs to a ClassB" (or "a ClassA is a class of (type) ClassB") or even "a ClassA is (also) a ClassB" is more appropriate. But the first is not implemented and the second only works with objects, just like the instanceof operator.
Plus, I just have tested your code and it does absolutely NOT do the same as instanceof (extended to classes)! I can't advise anyone to reuse it. The use of <?php is_instance_of ($instanceOfA, 'ClassB'); ?> raises a warning "include_once(Object id #1.php) …" when using __autoload (trying to look for $instanceOfA as if it was a class name).
Finally, here is a fast (to me) sample function code to verify if an object or class:
<?php
function kind_of (&$object_or_class, $class)
{
return is_object ($object_or_class) ?
$object_or_class instanceof $class
: (is_subclass_of ($object_or_class $class)
|| strtolower ($object_or_class) == strtolower ($class));
}
?>
jphaas at gmail dot com
11-Jul-2007 07:50
11-Jul-2007 07:50
Posting this so the word typeof appears on this page, so that this page will show up when you google 'php typeof'. ...yeah, former Java user.
vinyanov at poczta dot onet dot pl
20-Jun-2007 12:57
20-Jun-2007 12:57
Unfortunately the instanceof operator will not accept a string as its first operand. So I wrote this function. It does exactly the same (ie, successively checks identicalness, inheritance and implementation). Just on strings.
<?php
function is_instance_of($sub, $super)
{
$sub = (string)$sub;
$super = is_object($super) ? get_class($super) : (string)$super;
switch(true)
{
case $sub === $super; // well ... conformity
case is_subclass_of($sub, $super):
case in_array($super, class_implements($sub)):
return true;
default:
return false;
}
}
// testing
interface X {}
class A {}
class B extends A {}
class C extends B {}
class D implements X {}
$i = 'is_instance_of';
var_dump($i('A', 'A'), $i('B', 'A'), $i('C', 'A'), $i('D', 'X'));
?>
jeanyves dot terrien at orange-ftgroup dot com
13-Mar-2007 09:34
13-Mar-2007 09:34
Cross version function even if you are working in php4
(instanceof is an undefined operator for php4)
function isMemberOf($classename) {
$ver = floor(phpversion());
if($ver > 4) {
$instanceof = create_function ('$obj,$classname','return $obj instanceof $classname;');
return $instanceof($this,$classname);
} else {
// Php4 uses lowercase for classname.
return is_a($this, strtolower($classname));
}
} // end function isMemberOf
soletan at toxa dot de
03-Mar-2007 01:04
03-Mar-2007 01:04
Please note: != is a separate operator with separate semantics. Thinking about language grammar it's kind of ridicilous to negate an operator. Of course, it's possible to negate the result of a function (like is_a()), since it isn't negating the function itself or its semantics.
instanceof is a binary operator, and so used in binary terms like this
terma instanceof termb
while ! (negation) is a unary operator and so may be applied to a single term like this
!term
And a term never consists of an operator, only! There is no such construct in any language (please correct me!). However, instanceof doesn't finally support nested terms in every operand position ("terma" or "termb" above) as negation does:
!!!!!!!!!!!!!!term == term
So back again, did you ever write
a !!!!!!!!!!!!= b
to test equivalence?
mikael dot knutsson at gmail dot com
06-Dec-2006 05:34
06-Dec-2006 05:34
I can confirm what thisbizness at gmail dot com said just below in PHP 5.2, furthermore, people looking to use this as a "if $a is not instance of A" for error throwing purposes or other, just type it like this:
<?php
if( !$a instanceof A ) {
throw new Exception( '$a is not instance of A.' );
}
?>
This also works if $a is not an object, or not even set (you will get an E_NOTICE if it isn't set though).
A note worth making is that if you are unsure of if class A is present when making this comparison, and you don't want to trigger the __autoload() magic method, scroll down for examples of how to get around this.
I was unsure about it at first since most other operators have their own negative (like !=) or they are/can be used as function calls (like !is_a()) but it is this simple. Hope it helps someone.
Until again!
archanglmr at yahoo dot com
18-Feb-2005 03:37
18-Feb-2005 03:37
Negated instanceof doesn't seem to be documented. When I read instanceof I think of it as a compairson operator (which I suppose it's not).
<?php
class A {}
class X {}
//parse error from !
if (new X !instanceof A) {
throw new Exception('X is not an A');
}
//proper way to negate instanceof ?
if (!(new X instanceof A)) {
throw new Exception('X is not an A');
}
?>
d dot schneider at 24you dot de
18-Dec-2004 09:42
18-Dec-2004 09:42
use this for cross-version development...
<?php
function is_instance_of($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;
}
}
?>