Autoloading Classes

Muitos desenvolvedores ao desenvolver aplicações orientadas a objeto criam um arquivo PHP para cada definição de classe. Um dos maiores contratempos é ter de escrever uma longa lista de includes no início de cada script(um para cada classe).

A função spl_autoload_register() registra qualquer número de autoloaders, permitindo que classes e interfaces sejam automaticamente carregadas se elas não ainda não foram definidas. Ao registrar autoloaders, o PHP têm uma última chance de carregar classes e interfaces antes que falhem com um erro.

Qualquer construto tipo classe pode ser automaticamente carregado do mesmo jeito. Isso inclui classes, interfaces, traits, and enumerações.

Cuidado

Antes do PHP 8.0.0. era possível usar __autoload() para fazer autoload de classes and interfaces. No entanto, ela é uma alternativa menos flexível a spl_autoload_register() e __autoload() está depreciada a partir do PHP 7.2.0, e removida a partir do PHP 8.0.0.

Nota:

spl_autoload_register() pode ser chamada várias vezes para registrar múltiplos autoloaders. No entando, lançar uma exceção em uma função de autoload interromperá esse processo e não permitirá que outras funções de autoload sejam executadas. Por esse motivo, o lançamento de exceções em funções de autoload é altamente desencorajado.

Exemplo #1 Exemplo de Autoload

Esse exemplo tenta carregar as classes MyClass1 e MyClass2 dos arquivos MyClass1.php e MyClass2.php respectivamente.

<?php
spl_autoload_register
(function ($class_name) {
    include 
$class_name '.php';
});

$obj  = new MyClass1();
$obj2 = new MyClass2();
?>

Exemplo #2 Outro exemplo de Autoload

Este exemplo tenta carregar a interface ITest.

<?php

spl_autoload_register
(function ($name) {
    
var_dump($name);
});

class 
Foo implements ITest {
}

/*
string(5) "ITest"

Fatal error: Interface 'ITest' not found in ...
*/
?>

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User Contributed Notes 5 notes

up
96
jarret dot minkler at gmail dot com
13 years ago
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.
up
58
str at maphpia dot com
5 years ago
This 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();
up
19
toi]n[enkayt[attaat]gmaal.com
2 years ago
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 ();
?>
up
11
Anonymous
12 years ago
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.php
up
2
kalkamar at web dot de
13 years ago
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'));
?>
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