PHP 8.4.0 RC2 available for testing

class_alias

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

class_aliasCreates an alias for a class

Description

class_alias(string $class, string $alias, bool $autoload = true): bool

Creates an alias named alias based on the user defined class class. The aliased class is exactly the same as the original class.

Note: As of PHP 8.3.0, class_alias() also supports creating an alias of a PHP internal class.

Parameters

class

The original class.

alias

The alias name for the class.

autoload

Whether to autoload if the original class is not found.

Return Values

Returns true on success or false on failure.

Changelog

Version Description
8.3.0 class_alias() now supports creating an alias of an internal class.

Examples

Example #1 class_alias() example

<?php

class Foo { }

class_alias('Foo', 'Bar');

$a = new Foo;
$b = new Bar;

// the objects are the same
var_dump($a == $b, $a === $b);
var_dump($a instanceof $b);

// the classes are the same
var_dump($a instanceof Foo);
var_dump($a instanceof Bar);

var_dump($b instanceof Foo);
var_dump($b instanceof Bar);

?>

The above example will output:

bool(true)
bool(false)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)

Notes

Note:

Class names are case-insensitive in PHP, and this is reflected in this function. Aliases created by class_alias() are declared in lowercase. This means that for a class MyClass, the class_alias('MyClass', 'MyClassAlias') call will declare a new class alias named myclassalias.

See Also

add a note

User Contributed Notes 14 notes

up
32
mweierophinney at gmail dot com
11 years ago
class_alias() gives you the ability to do conditional imports.

Whereas the following will not work:

<?php
namespace Component;

if (
version_compare(PHP_VERSION, '5.4.0', 'gte')) {
use
My\ArrayObject;
} else {
use
ArrayObject;
}

class
Container extends ArrayObject
{
}
?>

the following, using class_alias, will:

<?php
namespace Component;

if (
version_compare(PHP_VERSION, '5.4.0', 'lt')) {
class_alias('My\ArrayObject', 'Component\ArrayObject');
} else {
class_alias('ArrayObject', 'Component\ArrayObject');
}

class
Container extends ArrayObject
{
}
?>

The semantics are slightly different (I'm now indicating that Container extends from an ArrayObject implementation in the same namespace), but the overall idea is the same: conditional imports.
up
11
robsonvnasc at gmail dot com
8 years ago
It also works with Traits!

<?php
trait Foo {}
class_alias("Foo","Bar");
echo
trait_exists("Bar") ? 'yes' : 'no';
?>
//yes
up
17
nicolas dot grekas+php at gmail dot com
13 years ago
class_alias also works for interfaces!

<?php
interface foo {}
class_alias('foo', 'bar');
echo
interface_exists('bar') ? 'yes!' : 'no'; // prints yes!
?>
up
16
programmer-comfreek at hotmail dot com
13 years ago
If you defined the class 'original' in a namespace, you will have to specify the namespace(s), too:
<?php
namespace ns1\ns2\ns3;

class
A {}

class_alias('ns1\ns2\ns3\A', 'B');
/* or if you want B to exist in ns1\ns2\ns3 */
class_alias('ns1\ns2\ns3\A', 'ns1\ns2\ns3\B');
?>
up
2
elliseproduction at gmail dot com
4 years ago
You can add a alias inside a class :

<?php

class foo{

function
__construct(){

echo(
'yes!');

}
}

class
bar {

function
__construct(){

class_alias('foo', 'fooAlias');

}

function
test(){

new
fooAlias;

}

}

$bar=new bar;

$bar->test(); // yes!
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5
stanislav dot eckert at vizson dot de
9 years ago
class_alias() creates aliases only for user defined classes, not for classes supplied by PHP (PHP will show the warning "First argument of class_alias() must be a name of user defined class"). To create aliases for every kind of classes, use namespaces:

<?php

// Does not work
class_alias("ZipArchive", "myZip");

// Creates class alias "myZip" of class "ZipArchive"
use \ZipArchive as myZip;

?>
up
1
Hayley Watson
6 years ago
The alias really is an alias for the existing class. It's not a new class of any kind - whether by inheritance or otherwise; it doesn't just look and behave exactly like the existing class; it really is the same class.

<?php

class foo
{
public static
$count = 0;
}

class_alias('foo', 'bar');

bar::$count++;

echo
foo::$count; // Output: 1

echo get_class(new Bar); // Output: foo
?>
Note in the last line there that aliases are just as case-insensitive as "genuine" class names.
up
1
sergey dot karavay at gmail dot com
11 years ago
At first, you might wonder that:
<?php class A {}; class_alias('A', 'B'); ?>

is equivalent to:
<?php class A {}; class B extends A {}; ?>

class_alias is NOT equivalent to class extending! Private methods/properties are unseen in child classes, but in alias classes they are.
up
1
Anonymous
3 years ago
Check is alias:
<?php
/**
* @param string $class Class name
* @return bool
*/
function is_alias(string $class): bool
{
return
$class !== (new ReflectionClass($class))->name;
}
?>
Get class aliases:
<?php
/**
* @param string $class Class name
* @param bool $throw Throw exception at error?
* @return string[]|null Aliases or null at error in silent mode
* @throws InvalidArgumentException Class not exists or it's alias
*/
function get_class_aliases(string $class, bool $throw = false): ?array
{
/**
* @var array An array of defined classes: keys - classes, values - aliases
*/
static $classes = [];
// check: class exists
if (! class_exists($class, true)) {
if (
$throw) {
throw new
InvalidArgumentException('Class ' . $class . ' not exists');
}
return
null;
}
// refresh list
$newClasses = array_diff(get_declared_classes(), array_keys($classes));
if (
$newClasses) {
$abc = range('a', 'z');
foreach (
$newClasses as $newClass) {
// fast check first char: class_alias() convert alias to lower case
if (in_array($newClass[0], $abc, true)) {
$realClass = (new ReflectionClass($newClass))->getName();
$classes[$newClass] = $newClass !== $realClass ? $realClass : null;
} else {
$classes[$newClass] = null;
}
}
unset(
$abc, $newClasses);
}
// check: is alias?
if (! empty($classes[$class])) {
if (
$throw) {
throw new
InvalidArgumentException($class . ' is alias for class ' . $classes[$class]);
}
return
null;
}
// find aliases
return array_keys($classes, $class, true);
}
?>
Usage:
<?php
class Foo {}
class_alias('Foo', 'Bar');
class_alias('Bar', 'Baz');
$aliases = get_class_aliases('Foo', true); // ['bar', 'baz']
?>
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0
info at ensostudio dot ru
4 years ago
Note: this function set alias for user classes, you can't use something like this
<?php
class_alias
('ArrayObject', 'ArrObj');
?>
up
0
adam at adamhahn dot com
13 years ago
Something to note,

If the $original class has not yet been defined or loaded, the auto loader will be invoked in order to try and load it.

If the class for which you are trying to create an alias does not exist, or can not be loaded with the auto loader, you will generate a PHP Warning.
up
0
nicolas dot grekas+php at gmail dot com
13 years ago
At first, you might wonder that:
<?php class A {}; class_alias('A', 'B'); ?>

is equivalent to:
<?php class A {}; class B extends A {}; ?>

BUT when derivation creates a new class name - that means, you can then instantiate a new kind of objects - aliasing is just what it says: a synonym, so objects instantiated with the aliased name are of the exact same kind of objects instantiated with the non-aliased name.

See this code for example:
<?php
class A {};
class
B1 extends A {};
class_alias('A', 'B2');

$b1 = new B1; echo get_class($b1); // prints B1
$b2 = new B2; echo get_class($b2); // prints A !
?>
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-3
sofe2038 at gmail dot com
7 years ago
Doesn't work with coupled classes when used along with autoloading.

For example, in these classes where each class is autoloaded in a separate class file:

Foo.php:

<?php
interface Foo{
public function
fx(Bar $bar);
}
?>

Bar2.php:

<?php
class Bar2 implements Foo{
public function
fx(Bar2 $bar){
// some implementation code here
}
}
?>

Bar.php:

<?php
class_alias
("Bar2", "Bar");
?>

When used with an autoloader like this:

<?php
spl_autoload_register
(function($class){
require(
$class . ".php");
});
new
Bar;
?>

Results in fatal error:

Declaration of Bar2::fx(Bar2 $bar) must be compatible with Foo::fx(Bar $bar) in ~/Bar2.php on line 2
up
-4
sofe2038 at gmail dot com
7 years ago
Doesn't work with coupled classes when used along with autoloading.

For example, in these classes where each class is autoloaded in a separate class file:

Foo.php:

<?php
interface Foo{
public function
fx(Bar $bar);
}
?>

Bar2.php:

<?php
class Bar2 implements Foo{
public function
fx(Bar2 $bar){
// some implementation code here
}
}
?>

Bar.php:

<?php
class_alias
("Bar2", "Bar");
?>

When used with an autoloader like this:

<?php
spl_autoload_register
(function($class){
require(
$class . ".php");
});
new
Bar;
?>

Results in fatal error:

Declaration of Bar2::fx(Bar2 $bar) must be compatible with Foo::fx(Bar $bar) in ~/Bar2.php on line 2
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