autoload.php

<?php
/**
 * Copyright 2014 Facebook, Inc.
 *
 * You are hereby granted a non-exclusive, worldwide, royalty-free license to
 * use, copy, modify, and distribute this software in source code or binary
 * form for use in connection with the web services and APIs provided by
 * Facebook.
 *
 * As with any software that integrates with the Facebook platform, your use
 * of this software is subject to the Facebook Developer Principles and
 * Policies [http://developers.facebook.com/policy/]. This copyright notice
 * shall be included in all copies or substantial portions of the software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 */

/**
 * You only need this file if you are not using composer.
 * Why are you not using composer?
 * https://getcomposer.org/
 */

if (version_compare(PHP_VERSION, '5.4.0', '<')) {
  throw new Exception('The Facebook SDK v4 requires PHP version 5.4 or higher.');
}

/**
 * Register the autoloader for the Facebook SDK classes.
 * Based off the official PSR-4 autoloader example found here:
 * https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader-examples.md
 *
 * @param string $class The fully-qualified class name.
 * @return void
 */
spl_autoload_register(function ($class)
{
  // project-specific namespace prefix
  $prefix = 'Facebook\\';

  // base directory for the namespace prefix
  $base_dir = defined('FACEBOOK_SDK_V4_SRC_DIR') ? FACEBOOK_SDK_V4_SRC_DIR : __DIR__ . '/src/Facebook/';

  // does the class use the namespace prefix?
  $len = strlen($prefix);
  if (strncmp($prefix, $class, $len) !== 0) {
    // no, move to the next registered autoloader
    return;
  }

  // get the relative class name
  $relative_class = substr($class, $len);

  // replace the namespace prefix with the base directory, replace namespace
  // separators with directory separators in the relative class name, append
  // with .php
  $file = $base_dir . str_replace('\\', '/', $relative_class) . '.php';

  // if the file exists, require it
  if (file_exists($file)) {
    require $file;
  }
});