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.
class_alias
(PHP 5 >= 5.3.0, PHP 7)
class_alias — Creates an alias for a class
Description
class_alias
( string
$original
, string $alias
[, bool $autoload = TRUE
] ) : bool
Creates an alias named alias
based on the user defined class original.
The aliased class is exactly the same as the original class.
Parameters
-
original -
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.
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)
See Also
- get_parent_class() - Retrieves the parent class name for object or class
- is_subclass_of() - Checks if the object has this class as one of its parents or implements it
add a note
User Contributed Notes 13 notes
mweierophinney at gmail dot com ¶
6 years ago
programmer-comfreek at hotmail dot com ¶
8 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');
?>
nicolas dot grekas+php at gmail dot com ¶
8 years ago
class_alias also works for interfaces!
<?php
interface foo {}
class_alias('foo', 'bar');
echo interface_exists('bar') ? 'yes!' : 'no'; // prints yes!
?>
stanislav dot eckert at vizson dot de ¶
4 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;
?>
sergey dot karavay at gmail dot com ¶
6 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.
nicolas dot grekas+php at gmail dot com ¶
8 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 !
?>
robsonvnasc at gmail dot com ¶
3 years ago
It also works with Traits!
<?php
trait Foo {}
class_alias("Foo","Bar");
echo trait_exists("Bar") ? 'yes' : 'no';
?>
//yes
Hayley Watson ¶
1 year 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.
sofe2038 at gmail dot com ¶
2 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
sofe2038 at gmail dot com ¶
2 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
adam at adamhahn dot com ¶
8 years ago
Something to note,
If the $original class has not yet been defined or loaded, the auto loader will be invoked in order to try and load it.
If the class for which you are trying to create an alias does not exist, or can not be loaded with the auto loader, you will generate a PHP Warning.
petar dot karan dot pk at gmail dot com ¶
5 years ago
If you need the same function in PHP version < 5.3 you can use this
<?php
function class_alias($original,$alias) {
$newclass = create_function('','class '.$alias.' extends '.$original.' {}');
$newclass();
}
?>
Anonymous ¶
6 years ago
Like class_alias but for functions:
<?php
function function_alias ($original, $alias) {
$args = func_get_args();
assert('count($args) == 2', 'function_alias() require exactly two arguments');
assert('is_string($original) && is_string($alias)', 'function_alias() require string arguments');
// valid function name - http://php.net/manual/en/functions.user-defined.php
assert('preg_match(\'/^[a-zA-Z_\x7f-\xff][\\\\\\\\a-zA-Z0-9_\x7f-\xff]*$/\', $original) > 0',
"'$original' is not a valid function name");
assert('preg_match(\'/^[a-zA-Z_\x7f-\xff][\\\\\\\\a-zA-Z0-9_\x7f-\xff]*$/\', $alias) > 0',
"'$alias' is not a valid function name");
$aliasNamespace = substr($alias, 0, strrpos($alias, '\\') !== false ? strrpos($alias, '\\') : 0);
$aliasName = substr($alias, strrpos($alias, '\\') !== false ? strrpos($alias, '\\') + 1 : 0);
$serializedOriginal = var_export($original, true);
eval("
namespace $aliasNamespace {
function $aliasName () {
return call_user_func_array($serializedOriginal, func_get_args());
}
}
");
}
?>
Until hopefully function_alias is added to php...
