Autoloading Classes
Many developers writing object-oriented applications create one PHP source file per class definition. One of the biggest annoyances is having to write a long list of needed includes at the beginning of each script (one for each class).
In PHP 5, this is no longer necessary. You may define an __autoload() function which is automatically called in case you are trying to use a class/interface which hasn't been defined yet. By calling this function the scripting engine is given a last chance to load the class before PHP fails with an error.
spl_autoload_register() provides a more flexible alternative for autoloading classes. For this reason, using __autoload() is discouraged and may be deprecated or removed in the future.
Note:
Prior to 5.3.0, exceptions thrown in the __autoload function could not be caught in the catch block and would result in a fatal error. From 5.3.0+ exceptions thrown in the __autoload function can be caught in the catch block, with 1 provision. If throwing a custom exception, then the custom exception class must be available. The __autoload function may be used recursively to autoload the custom exception class.
Note:
Autoloading is not available if using PHP in CLI interactive mode.
Note:
If the class name is used e.g. in call_user_func() then it can contain some dangerous characters such as ../. It is recommended to not use the user-input in such functions or at least verify the input in __autoload().
Example #1 Autoload example
This example attempts to load the classes MyClass1 and MyClass2 from the files MyClass1.php and MyClass2.php respectively.
<?php
function __autoload($class_name) {
include $class_name . '.php';
}
$obj = new MyClass1();
$obj2 = new MyClass2();
?>
Example #2 Autoload other example
This example attempts to load the interface ITest.
<?php
function __autoload($name) {
var_dump($name);
}
class Foo implements ITest {
}
/*
string(5) "ITest"
Fatal error: Interface 'ITest' not found in ...
*/
?>
Example #3 Autoloading with exception handling for 5.3.0+
This example throws an exception and demonstrates the try/catch block.
<?php
function __autoload($name) {
echo "Want to load $name.\n";
throw new Exception("Unable to load $name.");
}
try {
$obj = new NonLoadableClass();
} catch (Exception $e) {
echo $e->getMessage(), "\n";
}
?>
The above example will output:
Want to load NonLoadableClass. Unable to load NonLoadableClass.
Example #4 Autoloading with exception handling for 5.3.0+ - Missing custom exception
This example throws an exception for a non-loadable, custom exception.
<?php
function __autoload($name) {
echo "Want to load $name.\n";
throw new MissingException("Unable to load $name.");
}
try {
$obj = new NonLoadableClass();
} catch (Exception $e) {
echo $e->getMessage(), "\n";
}
?>
The above example will output:
Want to load NonLoadableClass. Want to load MissingException. Fatal error: Class 'MissingException' not found in testMissingException.php on line 4
- Введение
- Основы
- Свойства
- Константы классов
- Автоматическая загрузка классов
- Конструкторы и деструкторы
- Область видимости
- Наследование
- Оператор разрешения области видимости (::)
- Ключевое слово "static"
- Абстрактные классы
- Интерфейсы объектов
- Трейты
- Anonymous classes
- Перегрузка
- Итераторы объектов
- Магические методы
- Ключевое слово "final"
- Клонирование объектов
- Сравнение объектов
- Контроль типа
- Позднее статическое связывание
- Объекты и ссылки
- Сериализация объектов
- Журнал изменений ООП
Коментарии
Because static classes have no constructor I use this to initialize such classes.
The function init will (if available) be called when you first use the class.
The class must not be included before, otherwise the init-function wont be called as autoloading is not used.
<?php
function __autoload($class_name)
{
require_once(CLASSES_PATH.$class_name.'.cls.php');
if(method_exists($class_name,'init'))
call_user_func(array($class_name,'init'));
return true;
}
?>
I use it for example to establish the mysql-connection on demand.
It is also possilbe do add a destructor by adding this lines to the function:
<?php
if(method_exists($class_name,'destruct'))
register_shutdown_function(array($class_name,'destruct'));
?>
You should not have to use require_once inside the autoloader, as if the class is not found it wouldn't be trying to look for it by using the autoloader.
Just use require(), which will be better on performance as well as it does not have to check if it is unique.
It's worth to mention, if your operating system is case-sensitive you need to name your file with same case as in source code eg. MyClass.php instead of myclass.phpThis is my autoloader for my PSR-4 clases. I prefer to use composer's autoloader, but this works for legacy projects that can't use composer.
<?php
/**
* Simple autoloader, so we don't need Composer just for this.
*/
class Autoloader
{
public static function register()
{
spl_autoload_register(function ($class) {
$file = str_replace('\\', DIRECTORY_SEPARATOR, $class).'.php';
if (file_exists($file)) {
require $file;
return true;
}
return false;
});
}
}
Autoloader::register();
Autoloading plain functions is not supported by PHP at the time of writing. There is however a simple way to trick the autoloader to do this. The only thing that is needed is that the autoloader finds the searched class (or any other autoloadable piece of code) from the files it goes through and the whole file will be included to the runtime.
Let's say you have a namespaced file for functions you wish to autoload. Simply adding a class of the same name to that file with a single constant property is enough to trigger the autoloader to seek for the file. Autoloading can then be triggered by accessing the constant property.
The constant could be replaced by any static property or method or by default constructor. However, I personally find a constant named 'load' elegant and informative. After all this is a workaround. Another thing to keep in mind is that this introduces an unnecessary class to the runtime. The benefit of this is that there is no need to manually include or require files containing functions by path which in turn makes code maintaining easier. Such behaviour makes it easier to alter the project structure since manual includes need not to be fixed. Only the autoloader needs to be able to locate the moved files which can be automated.
A code file containing functions.
/Some/Namespace/Functions.php
<?php
namespace Some\Namespace;
class Functions { const load = 1; }
function a () {
}
function b () {
}
?>
Triggering autoloading of the file containing functions.
main.php
<?php
\Some\Namespace\Functions::load;
a ();
b ();
?>