PHP - most lightweight psr-0 compliant autoloader

Question

I have a tiny application that i need an autoloader for. I could easily use the symfony2 class loader but it seems like overkill.

Is there a stable extremely lightweight psr-0 autloader out there?

Answer 1

You ask extremely lightweight, let's do so ;)

Timothy Boronczyk wrote a nice minimal SPL autoloader : http://zaemis.blogspot.fr/2012/05/writing-minimal-psr-0-autoloader.html

I condensed the code like this:

function autoload1( $class ) {
    preg_match('/^(.+)?([^\\\\]+)$/U', ltrim( $class, '\\' ), $match ) );
    require str_replace( '\\', '/', $match[ 1 ] )
        . str_replace( [ '\\', '_' ], '/', $match[ 2 ] )
        . '.php';
}

Then compare (minified versions of) this [autoload3] with short @Alix Axel code [autoload4] :

function autoload3($c){preg_match('/^(.+)?([^\\\\]+)$/U',ltrim($c,'\\'),$m);require str_replace('\\','/',$m[1]).str_replace(['\\','_'],'/',$m[2]).'.php';}
function autoload4($c){require (($n=strrpos($c=ltrim($c,'\\'),'\\'))!==false?str_replace('\\','/',substr($c,0,++$n)):null).str_replace('_','/',substr($c,$n)).'.php';}

autoload3 is the shortest !

Let's use stable & extremely lightweight (175b !) autoloader file :

<?php spl_autoload_register(function ($c){preg_match('/^(.+)?([^\\\\]+)$/U',ltrim($c,'\\'),$m);require str_replace('\\','/',$m[1]).str_replace(['\\','_'],'/',$m[2]).'.php';});

Maybe i'm crazy but you Asked for extreme, no?

EDIT: Thanks to Alix Axel, i've shorten the code (only 100b !) and used include instead of require in case you have various autoloading strategy for old libs (and then various autoloader in spl autoload stack...).

<?php spl_autoload_register(function($c){@include preg_replace('#\\\|_(?!.+\\\)#','/',$c).'.php';});

If you want to make it shorter / better, please use this gist.

Answer 2

The PSR-0 specification document has an examplary compatible autoloader function that is already pretty short:

function autoload($className)
{
    $className = ltrim($className, '\\');
    $fileName  = '';
    $namespace = '';
    if ($lastNsPos = strripos($className, '\\')) {
        $namespace = substr($className, 0, $lastNsPos);
        $className = substr($className, $lastNsPos + 1);
        $fileName  = str_replace('\\', DIRECTORY_SEPARATOR, $namespace) . DIRECTORY_SEPARATOR;
    }
    $fileName .= str_replace('_', DIRECTORY_SEPARATOR, $className) . '.php';

    require $fileName;
}

It's usage is pretty straight forward:

spl_autoload_register('autoload');

The shortcoming with it is, that you need to configure base-directories it works on with the include_path directive. To support a hybrid PSR-0 autoloaders leaned onto SPL semantics, the following one supportss include path and spl autoload extensions:

$spl_autoload_register_psr0 = function ($extensions = null) 
{
    $callback = function ($className, $extensions = null) 
    {
        if (!preg_match('~^[a-z0-9\\_]{2,}$~i', $className)) {
            return;
        }
        null !== $extensions || $extensions = spl_autoload_extensions();
        $extensions = array_map('trim', explode(',', $extensions));
        $dirs = array_map('realpath', explode(PATH_SEPARATOR, get_include_path()));

        $classStub = strtr($className, array('_' => '/', '\\' => '/'));

        foreach ($dirs as $dir) {
            foreach ($extensions as $extension) {
                $file = sprintf('%s/%s%s', $dir, $classStub, $extension);
                if (!is_readable($file)) {
                    continue;
                }
                include $file;
                return;
            }
        }
    };

    return spl_autoload_register($callback);
};

The The Symfony2 ClassLoader Component has the benefit to allow more configuration here. You can install it easily via Pear or Composer (symfony/class-loader on Packagist). It is a component on it's own that is used by many and fairly well tested and supported.