is_a
(PHP 4 >= 4.2.0, PHP 5, PHP 7)
is_a — 如果对象属于该类或该类是此对象的父类则返回 TRUE
说明
$object
, string $class_name
[, bool $allow_string = FALSE
] )
如果 object 是该类或该类是此对象的父类。
参数
-
object -
The tested object
-
class_name -
The class name
-
allow_string -
If this parameter set to
FALSE, string class name asobjectis not allowed. This also prevents from calling autoloader if the class doesn't exist.
返回值
Returns TRUE if the object is of this class or has this class as one of
its parents, FALSE otherwise.
更新日志
| 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.
|
范例
Example #1 is_a() 例子
<?php
// define a class
class WidgetFactory
{
var $oink = 'moo' ;
}
// create a new object
$WF = new WidgetFactory ();
if ( is_a ( $WF , 'WidgetFactory' )) {
echo "yes, \$WF is still a WidgetFactory\n" ;
}
?> Example #2 在 PHP 5 中使用 instanceof 运算符
<?php
if ( $WF instanceof WidgetFactory ) {
echo 'Yes, $WF is a WidgetFactory' ;
}
?> 参见
- get_class() - 返回对象的类名
- get_parent_class() - 返回对象或类的父类名
- is_subclass_of() - 如果此对象是该类的子类，则返回 TRUE
用户评论:
[#1] portugal {at} jawira {dot} com [2015-06-12 21:32:03]
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:
<?php
$object = 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:
<?php
$object = new \stdClass();
var_dump($object instanceof '\stdClass'); // Parse error: syntax error, unexpected ''\stdClass'' (T_CONSTANT_ENCAPSED_STRING)
?>
[#2] eitan at mosenkis dot net [2012-01-12 13:09:26]
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.
[#3] Aron Budinszky [2011-09-07 04:21:55]
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:
https://bugs.php.net/bug.php?id=55475
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...
[#4] p dot scheit at zweipol dot net [2007-01-16 01:44:48]
At least in PHP 5.1.6 this works as well with Interfaces.
<?php
interface test {
public function A();
}
class TestImplementor implements test {
public function A () {
print "A";
}
}
$testImpl = new TestImplementor();
var_dump(is_a($testImpl,'test'));
?>
will return true
[#5] cesoid at yahoo dot com [2005-10-05 19:01:04]
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.