PHP迭代器实现斐波那契数列

<?php

class FibonacciIterator implements Iterator
{
    public function __construct($maxNum = 1000)
    {
        $this->MAX_NUM = $maxNum;
        $this->rewind();
    }

    public function rewind()
    {
        $this->pos = 0; // key
        $this->pre = 0; // previous
        $this->cur = 1; // current
    }

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

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

    public function valid()
    {
        return $this->pos < $this->MAX_NUM;
    }

    public function next()
    {
       $newpre = $this->cur; 
       $this->cur += $this->pre; 
       $this->pre = $newpre; 
       $this->pos++;
    }
}

$fibiter = new FibonacciIterator();

// Result: 0:1 1:1 2:2 3:3 4:5 5:8 6:13 ...
foreach ($fibiter as $key => $val) {
    echo $key . ':' . $val . " ";
}