is_a

(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

说明

bool is_a ( object $object , string $class_name )

如果对象是该类或该类是此对象的父类则返回 TRUE，否则返回 FALSE。

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";
}
?>

is_a() 函数已废弃，自 PHP 5 起请使用 instanceof 类型运算符。上例在 PHP 5 中会是这样：

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()，get_parent_class() 和 is_subclass_of()。

PHP手册 - N: 如果对象属于该类或该类是此对象的父类则返回 TRUE

用户评论:

webmaster at thedigitalorchard dot ca (14-Jan-2012 09:35)

What a farce, I must say. :) PHP 5.3.9 adds an $allow_string parameter in order to handle strings being passed in, but controls the auto-loading behavior? Talk about confusing. Not sure if there's a committee discussing changes to core functions like this, but I feel that's a poor design. Don't get me wrong, I greatly appreciate the voluntary efforts of PHP developers, but this loosy-goosy approach to function prototypes is a recipe for disaster over the long term.

eitan at mosenkis dot net (12-Jan-2012 09:09)

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.

Aron Budinszky (07-Sep-2011 12:21)

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...

p dot scheit at zweipol dot net (16-Jan-2007 09:44)

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

martin dunisch (13-Feb-2006 08:02)

Workaround for older PHP-Versions: function is_a($anObject, $aClass) { return get_class($anObject) == strtolower($aClass) or is_subclass_of($anObject, $aClass); }

dead dot screamer at seznam dot cz (06-Feb-2006 07:44)

Why I test if class `A` inherit class `B` or implements interface `C` before I create class `A`? <? //That isn't work: //1. function is_A() if(is_A('A','B'))$a=new A; if(is_A('A','C'))$a=new A; //2. operator instanceOf if(A instanceOf B)$a=new A; if(A instanceOf C)$a=new A; ?>

zabmilenko at hotmail dot com (08-Oct-2005 01:18)

Lazy Instantiation using is_a() and php5 <?php class ObjectA { public function print_line($text) { print $text . "\n"; } } class ObjectB { public function ObjectA() { static $objecta; if (!is_a($objecta, 'ObjectA')) { $objecta = new ObjectA; } return $objecta; } } $obj = new ObjectB; $obj->ObjectA()->print_line('testing, 1 2 3'); ?> In the above example, ObjectA is not instantiated until needed by ObjectB. Then ObjectB can continually use it's creation as needed without reinstantiating it. There are other ways, but I like this one :-)

cesoid at yahoo dot com (06-Oct-2005 03:01)

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.