迭代器模式

迭代器模式:提供一种方法顺序访问一个聚合对象中各个元素,而又不暴露该对象的内部表示.

<?php
/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2018/2/27
 * Time: 10:45
 */

namespace frontendmodels;


 abstract class Iterator
{

    public  abstract function First();

    public  abstract function  Next();

    public  abstract  function  IsDone();

    public  abstract  function  CurrentItem();

}

<?php
/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2018/2/27
 * Time: 10:47
 */

namespace frontendmodels;


class ConcreteIterator extends Iterator
{

    private  $arr;
    private  $current = 0;

    public  function  __construct($arr)
    {

         $this->arr = $arr;
    }

    //访问第一个元素
    public  function  First()
    {
        if (empty($this->arr))
            return null;

        return $this->arr[0];
    }

    //访问下一个元素
    public  function  Next()
    {
        $this->current++;

        if($this->current>count($this->arr)){

            return  $this->arr[$this->current];
        }

        return false;

    }

    //判断是否遍历完毕
    public  function  IsDone()
    {
        // TODO: Implement IsDone() method.

        return $this->current >= count($this->arr) ? true:false;
    }

    //返回当前聚集对象
    public  function  CurrentItem()
    {

        return $this->arr[$this->current];
    }

}

$iterator = new ConcreteIterator(['pig','dog','cat','fish','goose','swan','duck']);

echo $iterator->First()."<br>";

$iterator->Next();

echo $iterator->CurrentItem()."<br>";


 使用场景：   

         1.访问一个聚合对象的内容而无需暴露它的内部表示

         2.支持对聚合对象的多种遍历

         3.为遍历不同的聚合结构提供一个统一的接口