php 叠代器 iterator

介紹

可在內部叠代自己的外部叠代器或類的接口。

  
Iterator extends Traversable
{
    /* 方法 */
    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)
}

舉個栗子，定義一個叠代器：

class myIerator implements Iterator
{
    protected $position;//指針
    public $arr = [];

    public function __construct(array $arr)
    {
        $info = date('Y-m-d H:i:s') . ' ' . __METHOD__ . ' Line :' . __LINE__ . "\r\n";
        $this->writeLog($info);
        $this->arr = $arr;
        return $this;
    }

    //獲取當前的值
    public function current()
    {
        $info = date('Y-m-d H:i:s') . ' ' . __METHOD__ . ' Line :' . __LINE__ . "\r\n";
        $this->writeLog($info);
        return $this->arr[$this->position] ?? null;
    }

    //將指針移至下一位
    public function next()
    {
        $info = date('Y-m-d H:i:s') . ' ' . __METHOD__ . ' Line :' . __LINE__ . "\r\n";
        $this->writeLog($info);
        return ++$this->position;
    }

    //返回當前的指針
    public function key()
    {
        $info = date('Y-m-d H:i:s') . ' ' . __METHOD__ . ' Line :' . __LINE__ . "\r\n";
        $this->writeLog($info);
        return $this->position;
    }


    //重置指針
    public function rewind()
    {
        $info = date('Y-m-d H:i:s') . ' ' . __METHOD__ . ' Line :' . __LINE__ . "\r\n";
        $this->writeLog($info);
        $this->position = 0;
    }

    //檢查當前是否有效
    public function valid()
    {
        $info = date('Y-m-d H:i:s') . ' ' . __METHOD__ . ' Line :' . __LINE__ . "\r\n";
        $this->writeLog($info);
        return isset($this->arr[$this->position]);
    }

    private function writeLog(string $info)
    {
        error_log($info, 3, './debug.log');
    }
}

$zhangsan=['one','two','three','four'];
$arr = new myIerator($zhangsan);
foreach ($arr as $k => $v) {
    echo "{$k} => {$v} \r\n";
}

打印結果：

0 => one
1 => two
2 => three
3 => four

查看調用日誌：

2017-11-27 15:56:04 myIerator::__construct Line :16

2017-11-27 15:56:04 myIerator::rewind Line :50 重置指針

2017-11-27 15:56:04 myIerator::valid Line :58 校驗是否有效
2017-11-27 15:56:04 myIerator::current Line :25 獲取當前指針的值
2017-11-27 15:56:04 myIerator::key Line :41 獲取當前指針位置
2017-11-27 15:56:04 myIerator::next Line :33 指針下移一位（進入下一個循環）

2017-11-27 15:56:04 myIerator::valid Line :58
2017-11-27 15:56:04 myIerator::current Line :25

2017-11-27 15:56:04 myIerator::key Line :41
2017-11-27 15:56:04 myIerator::next Line :33

2017-11-27 15:56:04 myIerator::valid Line :58
2017-11-27 15:56:04 myIerator::current Line :25
2017-11-27 15:56:04 myIerator::key Line :41
2017-11-27 15:56:04 myIerator::next Line :33

2017-11-27 15:56:04 myIerator::valid Line :58
2017-11-27 15:56:04 myIerator::current Line :25
2017-11-27 15:56:04 myIerator::key Line :41
2017-11-27 15:56:04 myIerator::next Line :33

2017-11-27 15:56:04 myIerator::valid Line :58

//遍歷方式二：
$arr->rewind();
while ($arr->valid()) {
    $key = $arr->key();
    $value = $arr->current();

    echo "{$key} => {$value} \r\n";

    $arr->next();
}

PHP叠代器Iterator接口