is_a

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

is_aVerifica si el objeto es de un cierto tipo o subtipo.

Descripción

is_a(mixed $object_or_class, string $class, bool $allow_string = false): bool

Determina si el object_or_class dado es del tipo de objeto clase, o tiene clase como uno de sus supertipos.

Parámetros

object_or_class

Un nombre de clase o una instancia de un objeto.

class

El nombre de la clase o de la interfaz.

allow_string

Si este argumento vale false, el nombre de la clase en forma de string en el argumento object_or_class no está permitido. Esto permite evitar la llamada al autoloader si la clase no existe.

Valores devueltos

Retorna true si object_or_class es del tipo de objeto clase, o tiene clase como uno de sus supertipos, false en caso contrario.

Ejemplos

Ejemplo #1 Ejemplo con is_a()

<?php
// Define una clase
class WidgetFactory
{
var
$oink = 'moo';
}

// Crea un nuevo objeto
$WF = new WidgetFactory();

if (
is_a($WF, 'WidgetFactory')) {
echo
"sí, \$WF es siempre un objeto WidgetFactory\n";
}
?>

Ejemplo #2 Uso del operador instanceof

<?php

// definir una clase
class WidgetFactory
{
var
$oink = 'moo';
}

// crear un nuevo objeto
$WF = new WidgetFactory();

if (
$WF instanceof WidgetFactory) {
echo
'Sí, $WF es un WidgetFactory';
}
?>

Ver también

add a note

User Contributed Notes 7 notes

up
66
Ronald Locke
8 years ago
Please note that you have to fully qualify the class name in the second parameter.

A use statement will not resolve namespace dependencies in that is_a() function.

<?php
namespace foo\bar;

class
A {};
class
B extends A {};
?>

<?php
namespace har\var;

use
foo\bar\A;
$foo = new foo\bar\B();

is_a($foo, 'A'); // returns false;
is_a($foo, 'foo\bar\A'); // returns true;
?>

Just adding that note here because all examples are without namespaces.
up
34
Aron Budinszky
13 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:
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...
up
18
p dot scheit at zweipol dot net
18 years ago
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
up
4
SlimDeluxe
2 years ago
For anyone wondering, this does not work with traits :(
up
11
cesoid at yahoo dot com
19 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.
up
2
dkrupyanskiy[at]gmail
7 years ago
Looks like the function signature given in description is wrong. Actually it can take a string as a first parameter in the case if $allow_string is set to true.

It took some time to find out how the last parameter should be used. Please consider the following example

<?php

class Foo{}

spl_autoload_register(
function(
$classname){
printf('autoload has been triggered for %s%s', $classname, PHP_EOL);
}
);

var_dump(is_a('UndefinedClassName', Foo::class, true));

?>
up
2
eitan at mosenkis dot net
13 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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