(PHP 5 >= 5.3.0, PHP 7)
class_alias — Creates an alias for a class
$original
, string $alias
[, bool $autoload = TRUE
] )
Creates an alias named alias
based on the user defined class original.
The aliased class is exactly the same as the original class.
originalThe original class.
aliasThe alias name for the class.
autoloadWhether to autoload if the original class is not found.
Returns TRUE on success or FALSE on failure.
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)
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');
?>
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 also works for interfaces!
<?php
interface foo {}
class_alias('foo', 'bar');
echo interface_exists('bar') ? 'yes!' : 'no'; // prints yes!
?>
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;
?>
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.
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 !
?>
Something to note,
If the $original class has not yet been defined or loaded, the auto loader will be invoked in order to try and load it.
If the class for which you are trying to create an alias does not exist, or can not be loaded with the auto loader, you will generate a PHP Warning.
Like class_alias but for functions:
<?php
function function_alias ($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...
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.' {}');
$newclass();
}
?>
This function will appear in PHP 5.3 (at least I can use it with PHP 5.3, build Aug 7 2009 08:21:14)
For older versions of PHP I wrote the next function:
<?php
if (!function_exists('class_alias')) {
function class_alias($original, $alias) {
eval('abstract class ' . $alias . ' extends ' . $original . ' {}');
}
}
?>
Keyword 'abstract' is used for classes, which defines abstract methods.
This function is used in autoload purposes (when I extend classes), so abstract keyword doesn't broke anything for me.
