Problems with autoloading classes via sp_autoload_register / maybe interfering WP-specific autoloader

Question

I'm working on a plugin in which I do the following for autoloading classes:

function TFSLAutoload($class) {
    $classfile = dirname(__FILE__).'/includes/'.strtolower($class).'.php';
    include $classfile;
} // function TFSLAutoload
spl_autoload_register('TFSLAutoload');

In the plugin (classes) I can instantiate classes (e.g., use $myClassXYZ = new MyClassXYZ();) as well as use static functions (e.g., MyClassXYZ::my_static_func();) without including/requiring the file defining the very class. In short, everything is working as expected.

However, when having WP_DEBUG set to true, I do get the following warnings:

Warning: include(/var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/includes/wp_atom_server.php): failed to open stream: No such file or directory in /var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/tf-song-list.php on line 31 
Warning: include(): Failed opening '/var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/includes/wp_atom_server.php' for inclusion (include_path='.:') in /var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/tf-song-list.php on line 31 
Warning: include(/var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/includes/Recursive_ArrayAccess.php): failed to open stream: No such file or directory in /var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/tf-song-list.php on line 31 
Warning: include(): Failed opening '/var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/includes/Recursive_ArrayAccess.php' for inclusion (include_path='.:') in /var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/tf-song-list.php on line 31
Warning: include(/var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/includes/WP_Session.php): failed to open stream: No such file or directory in /var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/tf-song-list.php on line 31 
Warning: include(): Failed opening '/var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/includes/WP_Session.php' for inclusion (include_path='.:') in /var/www/vhosts/MY-DOMAIN.TLD/wp-content/plugins/tf-song-list/tf-song-list.php on line 31

I then changed my autoload function to check first if the file exists:

function TFSLAutoload($class) {
    $classfile = dirname(__FILE__).'/includes/'.strtolower($class).'.php';
    if (file_exists($classfile)) include $classfile;
    else echo "File »$classfile« does not exist.".PHP_EOL;
} // function TFSLAutoload
spl_autoload_register('TFSLAutoload');

Now, only my own plugin class files are loaded by the autoloader, as they are the only files loacted in the pre-defined folder.

However, if the three mentioned WordPress classes are still being 'sent' through my autolaoder class, are they even(tually) loaded correctly by WP? Or is my autoloader competing with the built-in autoloader of WP? How can I check that? Or: Am I doing the whole autoloading stuff the wrong way?

And why are these three classes sent to my autoloader? Are they the only ones to be load after the plugins are loaded?

Answer 1

There is no built-in autoloader in WordPress. But other plugins or a theme might have registered an autoloader, and depending on the order of execution these are called earlier or later than yours.

The only way to make sure the called class is in your code’s responsibility is checking with file_exists() and testing the class name.

file_exists() is slow and its result is cached by the file system, so you cannot rely on it anyway.

I recommend not to use an autoloader. Use a plugin specific class loader instead.

Example:

/**
 * Load a class from /php/ directory.
 *
 * There is no file_exists() check to improve performance.
 *
 * @param  string  $class         Class name
 * @param  boolean $create_object Return an object or TRUE
 * @return bool|$class
 */
function t5_es_load_class( $class, $create_object = FALSE )
{
    // create the path base just once
    static $base = FALSE;

    ! $base && $base = plugin_dir_path( __FILE__ ) . 'php';
    ! class_exists( $class ) && require "$base/class.$class.php";

    return $create_object ? new $class : TRUE;
}

Now you can use this function either to just include the class …

t5_es_load_class( 'T5_Metabox_Base' );
$metabox = new T5_Metabox_Base( 'preview' );

… or create an object …

$data               = t5_es_load_class( 'T5_Property_List', TRUE );
$data->plugin_url   = plugin_dir_url( __FILE__ );
$data->plugin_path  = plugin_dir_path( __FILE__ );

Faster, more reliable, more flexible.