Fibonnaci numbers generator

Fibonacci

<?php

// quick'n dirty

class Fibonacci implements Iterator {

    public function __construct () {
        $this->rewind();
    }

    public function __invoke () {
        $n = $this->current();
        $this->next();
        return $n;
    }

    public function current () {
        return $this->n;
    }

    public function key () {
        return $this->k;
    }

    public function next () {
        $this->k++;

        if ($this->k == 0)
            $this->n = 0;
        elseif ($this->k == 1)
            $this->n = 1;
        else {
            $this->n = $this->prev[0] + $this->prev[1];
            $this->prev[0] = $this->prev[1];
            $this->prev[1] = $this->n;
        }
    }
    
    public function rewind () {
        $this->n = 0;
        $this->k = 0;
        $this->prev = [0,1];
    }

    public function valid () {
        return true;
    }
}

$fibonacci_generator = new Fibonacci;

foreach (range(1,10) as $i)
    echo $fibonacci_generator() . "\n";

foreach (range(1,10) as $i)
    echo $fibonacci_generator() . "\n";