Sample of Inversion Of Control (IoC) and Singleton in PHP

IoC.php

<?php

class IoC {
  protected static $registry = array();
  protected static $shared = array();

  // Register
  public static function register($name, Closure $resolve)
  {
     static::$registry[$name] = $resolve;
  }

  // Singleton 
  public static function singleton($name, Closure $resolve)
  {
    static::$shared[$name] = $resolve();
  }

  // Resolve, consider register or singleton here
  public static function resolve($name)
  {
    if ( static::registered($name) )
    {
      $name = static::$registry[$name];
      return $name();
    }

    if ( static::singletoned($name) )
    {
      $instance = static::$shared[$name];
      return $instance;
    }
 
    throw new Exception('Nothing registered with that name, fool.');
  }

  // Check resigtered or not
  public static function registered($name)
  {
    return array_key_exists($name, static::$registry);
  }

  // Check singleton object or not
  public static function singletoned($name)
  {
    return array_key_exists($name, static::$shared);
  }

}
class Book {
    public $author;
    public function setAuthor($author)
    {
        $this->author = $author;
    }
    public function getAuthor()
    {
        return $this->author;
    }
}

// Register sample. Here $book1 and $book2 will end up with seperated instances of class Book
IoC::register('book',function(){
    $book = new Book;
    $book->setAuthor('DTVD');
    return $book;
});

$book1 = IoC::resolve('book');
$book2 = IoC::resolve('book');
echo "Register sample\n";
var_dump($book1===$book2);

// Singleton sample. Here $bookSingleton1 and $bookSingleton2 will end up with same instances of class Book
IoC::singleton('bookSingleton',function(){
    $book = new Book;
    $book->setAuthor('DTVD');
    return $book;
});

$bookSingleton1 = IoC::resolve('bookSingleton');
$bookSingleton2 = IoC::resolve('bookSingleton');
echo "Singleton sample\n";
var_dump($bookSingleton1===$bookSingleton2);