(PHP 5 >= 5.3.0)
class_alias — 为一个类创建别名
$original
, string $alias
[, bool $autoload = TRUE
] )
基于已定义的类 original 创建别名 alias。
这个别名类和原有的类完全相同。
original
原有的类。
alias
类的别名。
autoload
如果原始类没有加载，是否使用自动加载（autoload）。
成功时返回 TRUE， 或者在失败时返回 FALSE。
Example #1 class_alias() 例子
<?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($b instanceof bar);
?>
以上例程会输出：
bool(true) bool(false) bool(true) bool(true) bool(true) bool(true) bool(true)
mweierophinney at gmail dot com (2013-03-06 14:05:28)
class_alias() gives you the ability to do conditional imports.
Whereas the following will not work:
<?php
namespace Component;
if (version_compare(PHP_VERSION, '5.4.0', 'gte')) {
use My\ArrayObject;
} else {
use ArrayObject;
}
class Container extends ArrayObject
{
}
?>
the following, using class_alias, will:
<?php
namespace Component;
if (version_compare(PHP_VERSION, '5.4.0', 'lt')) {
class_alias('My\ArrayObject', 'Component\ArrayObject');
} else {
class_alias('ArrayObject', 'Component\ArrayObject');
}
class Container extends ArrayObject
{
}
?>
The semantics are slightly different (I'm now indicating that Container extends from an ArrayObject implementation in the same namespace), but the overall idea is the same: conditional imports.
sergey dot karavay at gmail dot com (2013-02-25 11:08:40)
At first, you might wonder that:
<?php class A {}; class_alias('A', 'B'); ?>
is equivalent to:
<?php class A {}; class B extends A {}; ?>
class_alias is NOT equivalent to class extending! Private methods/properties are unseen in child classes, but in alias classes they are.
Anonymous (2013-02-12 17:42:54)
Like class_alias but for functions:
<?php
function function_alias ($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...
adam at adamhahn dot com (2011-09-06 12:13:39)
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.
programmer-comfreek at hotmail dot com (2011-08-15 09:38:01)
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 (2010-12-31 01:09:56)
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 !
?>
nicolas dot grekas+php at gmail dot com (2010-12-30 14:41:14)
class_alias also works for interfaces!
<?php
interface foo {}
class_alias('foo', 'bar');
echo interface_exists('bar') ? 'yes!' : 'no'; // prints yes!
?>
paul [dot] kotets [at] gmail [dot] com (2009-09-03 03:43:21)
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.