PHPKonf İstanbul PHP Conference 2015


(PHP 4 >= 4.2.0, PHP 5)

is_a如果对象属于该类或该类是此对象的父类则返回 TRUE


bool is_a ( object $object , string $class_name [, bool $allow_string = FALSE ] )

如果 object 是该类或该类是此对象的父类。



The tested object


The class name


If this parameter set to FALSE, string class name as object is not allowed. This also prevents from calling autoloader if the class doesn't exist.


Returns TRUE if the object is of this class or has this class as one of its parents, FALSE otherwise.


版本 说明
5.3.9 Added allow_string parameter
5.3.0 This function is no longer deprecated, and will therefore no longer throw E_STRICT warnings.
5.0.0 This function became deprecated in favour of the instanceof operator. Calling this function will result in an E_STRICT warning.


Example #1 is_a() 例子

// define a class
class WidgetFactory
$oink 'moo';

// create a new object
$WF = new WidgetFactory();

if (
is_a($WF'WidgetFactory')) {
"yes, \$WF is still a WidgetFactory\n";

Example #2 在 PHP 5 中使用 instanceof 运算符

if ($WF instanceof WidgetFactory) {
'Yes, $WF is a WidgetFactory';


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User Contributed Notes 5 notes

Aron Budinszky
3 years ago
Be careful! Starting in PHP 5.3.7 the behavior of is_a() has changed slightly: when calling is_a() with a first argument that is not an object, __autoload() is triggered!

In practice, this means that calling is_a('23', 'User'); will trigger __autoload() on "23". Previously, the above statement simply returned 'false'.

More info can be found here:

Whether this change is considered a bug and whether it will be reverted or kept in future versions is yet to be determined, but nevertheless it is how it is, for now...
p dot scheit at zweipol dot net
8 years ago
At least in PHP 5.1.6 this works as well with Interfaces.

interface test {
  public function

TestImplementor implements test {
  public function
A () {

$testImpl = new TestImplementor();


will return true
cesoid at yahoo dot com
9 years ago
is_a returns TRUE for instances of children of the class.

For example:

class Animal

class Dog extends Animal

$test = new Dog();

In this example is_a($test, "Animal") would evaluate to TRUE as well as is_a($test, "Dog").

This seemed intuitive to me, but did not seem to be documented.
portugal {at} jawira {dot} com
25 days ago
I just want to point out that you can replace "is_a()" function with the "instanceof" operator, BUT you must use a variable to pass the class name string.

This will work:
= new \stdClass();
$class_name = '\stdClass';

var_dump(is_a($object, $class_name));     // bool(true)
var_dump(is_a($object, '\stdClass'));     // bool(true)
var_dump($object instanceof $class_name); // bool(true)

While this don't:
= new \stdClass();
var_dump($object instanceof '\stdClass'); // Parse error: syntax error, unexpected ''\stdClass'' (T_CONSTANT_ENCAPSED_STRING)
eitan at mosenkis dot net
3 years ago
As of PHP 5.3.9, is_a() seems to return false when passed a string for the first argument. Instead, use is_subclass_of() and, if necessary for your purposes, also check if the two arguments are equal, since is_subclass_of('foo', 'foo') will return false, while is_a('foo', 'foo') used to return true.
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