Autoloading in PHP

Autoloading feature

  1. Autoloading helps us to load the future classes without any pain (see: dozen of include or require),
  2. Can be implemented with spl_autoload_register() click
  3. Use PSR-4 autoloading click
  4. Codes to implement the functionality is here. click
  5. For single prefix namespaces first block
    
    <?php
    /**
    * An example of a project-specific implementation.
    *
    * After registering this autoload function with SPL, the following line
    * would cause the function to attempt to load the \Foo\Bar\Baz\Qux class
    * from /path/to/project/src/Baz/Qux.php:
    *
    *      new \Foo\Bar\Baz\Qux;
    *
    * @param string $class The fully-qualified class name.
    * @return void
    */
    if(!function_exists('version_compare') || version_compare(phpversion(), '5.1.0', '<'))die("Minimum version required for autoload is 5.1.0");
    spl_autoload_register(function ($class) {
    // project-specific namespace prefix
    $prefix = 'OSOLCCC\\';    
    // base directory for the namespace prefix
    $base_dir = dirname(__FILE__).DIRECTORY_SEPARATOR.'MVC/';
    //die($class . " " . str_replace($prefix,'',$class));
    // 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
    $mappedFile = $base_dir . str_replace('\\', '/', $relative_class) . '.php';
    try {
        if (file_exists($mappedFile)) {
            require $mappedFile;
        }
        else
        {
            //die('<p style="background:#f00">ERROR!!!!! file : '.$mappedFile. " does not exist to autoload for ".$class ."</p>");
            //throw new CustomException('ERROR!!!!! file : '.$mappedFile. " does not exist to autoload for ".$class );
            throw new Exception('ERROR!!!!! file : '.$mappedFile. " does not exist to autoload for ".$class );
        }
    }
    catch (Exception $e) {
      //display custom message
      $debug_trace = debug_backtrace();
      $fileAndLineno = "file : {$debug_trace[1]['file']} , Line #: {$debug_trace[1]['line']}";
      echo $e->getMessage() . $fileAndLineno;
    }
    });

?>

6. For multiple prefixes use the Psr4AutoloaderClass class

```php
<?php
namespace Example;

/**
 * An example of a general-purpose implementation that includes the optional
 * functionality of allowing multiple base directories for a single namespace
 * prefix.
 *
 * Given a foo-bar package of classes in the file system at the following
 * paths ...
 *
 *     /path/to/packages/foo-bar/
 *         src/
 *             Baz.php             # Foo\Bar\Baz
 *             Qux/
 *                 Quux.php        # Foo\Bar\Qux\Quux
 *         tests/
 *             BazTest.php         # Foo\Bar\BazTest
 *             Qux/
 *                 QuuxTest.php    # Foo\Bar\Qux\QuuxTest
 *
 * ... add the path to the class files for the \Foo\Bar\ namespace prefix
 * as follows:
 *
 *      <?php
 *      // instantiate the loader
 *      $loader = new \Example\Psr4AutoloaderClass;
 *
 *      // register the autoloader
 *      $loader->register();
 *
 *      // register the base directories for the namespace prefix
 *      $loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/src');
 *      $loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/tests');
 *
 * The following line would cause the autoloader to attempt to load the
 * \Foo\Bar\Qux\Quux class from /path/to/packages/foo-bar/src/Qux/Quux.php:
 *
 *      <?php
 *      new \Foo\Bar\Qux\Quux;
 *
 * The following line would cause the autoloader to attempt to load the
 * \Foo\Bar\Qux\QuuxTest class from /path/to/packages/foo-bar/tests/Qux/QuuxTest.php:
 *
 *      <?php
 *      new \Foo\Bar\Qux\QuuxTest;
 */
class Psr4AutoloaderClass
{
    /**
     * An associative array where the key is a namespace prefix and the value
     * is an array of base directories for classes in that namespace.
     *
     * @var array
     */
    protected $prefixes = array();

    /**
     * Register loader with SPL autoloader stack.
     *
     * @return void
     */
    public function register()
    {
        spl_autoload_register(array($this, 'loadClass'));
    }

    /**
     * Adds a base directory for a namespace prefix.
     *
     * @param string $prefix The namespace prefix.
     * @param string $base_dir A base directory for class files in the
     * namespace.
     * @param bool $prepend If true, prepend the base directory to the stack
     * instead of appending it; this causes it to be searched first rather
     * than last.
     * @return void
     */
    public function addNamespace($prefix, $base_dir, $prepend = false)
    {
        // normalize namespace prefix
        $prefix = trim($prefix, '\\') . '\\';

        // normalize the base directory with a trailing separator
        $base_dir = rtrim($base_dir, DIRECTORY_SEPARATOR) . '/';

        // initialize the namespace prefix array
        if (isset($this->prefixes[$prefix]) === false) {
            $this->prefixes[$prefix] = array();
        }

        // retain the base directory for the namespace prefix
        if ($prepend) {
            array_unshift($this->prefixes[$prefix], $base_dir);
        } else {
            array_push($this->prefixes[$prefix], $base_dir);
        }
    }

    /**
     * Loads the class file for a given class name.
     *
     * @param string $class The fully-qualified class name.
     * @return mixed The mapped file name on success, or boolean false on
     * failure.
     */
    public function loadClass($class)
    {
        // the current namespace prefix
        $prefix = $class;

        // work backwards through the namespace names of the fully-qualified
        // class name to find a mapped file name
        while (false !== $pos = strrpos($prefix, '\\')) {

            // retain the trailing namespace separator in the prefix
            $prefix = substr($class, 0, $pos + 1);

            // the rest is the relative class name
            $relative_class = substr($class, $pos + 1);

            // try to load a mapped file for the prefix and relative class
            $mapped_file = $this->loadMappedFile($prefix, $relative_class);
            if ($mapped_file) {
                return $mapped_file;
            }

            // remove the trailing namespace separator for the next iteration
            // of strrpos()
            $prefix = rtrim($prefix, '\\');
        }

        // never found a mapped file
        return false;
    }

    /**
     * Load the mapped file for a namespace prefix and relative class.
     *
     * @param string $prefix The namespace prefix.
     * @param string $relative_class The relative class name.
     * @return mixed Boolean false if no mapped file can be loaded, or the
     * name of the mapped file that was loaded.
     */
    protected function loadMappedFile($prefix, $relative_class)
    {
        // are there any base directories for this namespace prefix?
        if (isset($this->prefixes[$prefix]) === false) {
            return false;
        }
        // look through base directories for this namespace prefix
        foreach ($this->prefixes[$prefix] as $base_dir) {

            // 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 mapped file exists, require it
            if ($this->requireFile($file)) {
                // yes, we're done
                return $file;
            }
        }
        // never found it
        return false;
    }
    /**
     * If a file exists, require it from the file system.
     *
     * @param string $file The file to require.
     * @return bool True if the file exists, false if not.
     */
    protected function requireFile($file)
    {
        if (file_exists($file)) {
            require $file;
            return true;
        }
        return false;
    }
}
?>

AND use the block

require_once(__DIR__.'/Psr4AutoloaderClass.php');
// instantiate the loader
$loader = new \Example\Psr4AutoloaderClass;

// register the autoloader
$loader->register();

// register the base directories for the namespace prefix
/* $loader->addNamespace('Core\Controller', __DIR__.'/controller');
$loader->addNamespace('Core\View', __DIR__.'/view'); */
$loader->addNamespace('Core', __DIR__);
//$loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/tests');