Iterated Fibonacci Sequence in PHP

The Iterator is an interface for external iterators or objects that can be iterated themselves internally. In PHP, it is defined as follows.

Iterator extends Traversable 
{
  /* Methods */
  abstract public mixed current ( void )
  abstract public scalar key ( void )
  abstract public void next ( void )
  abstract public void rewind ( void )
  abstract public boolean valid ( void )
}

The following presents a simply clear example that computes the Fibonacci sequence using Iterator. The Fibonacci Number is very well known, probably due to its recursive definition. [read this]

Fibonacci Latex Equation

By implementing the above six methods, the following class can be used as a iterator, e.g. in the foreach statement. The valid tells if the current position is OK, if not, the foreach loop will terminate.

  class Fib implements Iterator 
  { 
    private $previous = 1; 
    private $current = 0; 
    private $key = 0; 
    
    public function __construct()
    {
        $this->rewind();
    }
       
    public function key() 
    { 
        return($this->key); 
    }

    public function current() 
    { 
        return($this->current); 
    } 
         
    public function next() 
    { 
        $n = $this->current; 
        $this->current += $this->previous; 
        $this->previous = $n; 
        $this->key++; 
    } 
    
    public function rewind() 
    { 
        $this->previous = 1; 
        $this->current = 0; 
        $this->key = 0; 
    } 
    
    public function valid() 
    { 
        return(true); 
    } 
  } 

  $seq = new Fib(); 
  $i = 0; 
  foreach ($seq as $f) 
  { 
    echo ($f); 
    if ($i++ === 10)
    {
      break;
    } 
  } 

–EOF (The Ultimate Computing & Technology Blog) —