PHP设计模式—迭代器模式

定义：

迭代器模式（Iterator）：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。

结构：

• Iterator：迭代器接口，用于定义得到开始对象、得到下一个对象、判断是否到有效、当前对象等抽象方法，统一接口，目前PHP已经集成有该类。
• IteratorAggregate：容器接口，目前PHP已经集成有该类。
• ConcreteAggregate：具体容器类，继承IteratorAggregate。
• ConcreteIterator：具体迭代器类，继承Iterator。
• Client：客户端代码。

代码实例：

/**
 * IteratorAggregate 源码
 * Interface to create an external Iterator.
 * @link https://php.net/manual/en/class.iteratoraggregate.php
 */
interface IteratorAggregate extends Traversable {

    /**
     * Retrieve an external iterator
     * @link https://php.net/manual/en/iteratoraggregate.getiterator.php
     * @return Traversable An instance of an object implementing <b>Iterator</b> or
     * <b>Traversable</b>
     * @since 5.0.0
     */
    public function getIterator();
}

/**
 * Iterator源码
 * Interface for external iterators or objects that can be iterated
 * themselves internally.
 * @link https://php.net/manual/en/class.iterator.php
 */
interface Iterator extends Traversable {

    /**
     * Return the current element
     * @link https://php.net/manual/en/iterator.current.php
     * @return mixed Can return any type.
     * @since 5.0.0
     */
    public function current();

    /**
     * Move forward to next element
     * @link https://php.net/manual/en/iterator.next.php
     * @return void Any returned value is ignored.
     * @since 5.0.0
     */
    public function next();

    /**
     * Return the key of the current element
     * @link https://php.net/manual/en/iterator.key.php
     * @return mixed scalar on success, or null on failure.
     * @since 5.0.0
     */
    public function key();

    /**
     * Checks if current position is valid
     * @link https://php.net/manual/en/iterator.valid.php
     * @return boolean The return value will be casted to boolean and then evaluated.
     * Returns true on success or false on failure.
     * @since 5.0.0
     */
    public function valid();

    /**
     * Rewind the Iterator to the first element
     * @link https://php.net/manual/en/iterator.rewind.php
     * @return void Any returned value is ignored.
     * @since 5.0.0
     */
    public function rewind();
}

/**
 * 具体聚集类
 * Class ConcreteAggregate
 */
class ConcreteAggregate implements \IteratorAggregate
{
    private $data = [];

    /**
     * 往迭代器里面添加数据
     */
    public function add($name)
    {
        $this->data[] = $name;
    }

    /**
     * 获取迭代器
     * @return ConcreteIterator|\Traversable
     */
    public function getIterator()
    {
        // TODO: Implement getIterator() method.
        return new ConcreteIterator($this->data);
    }
}

/**
 * 具体迭代器类
 * Class ConcreteIterator
 */
class ConcreteIterator implements \Iterator
{
    private $key = 0;
    private $data = [];

    public function __construct($data)
    {
        $this->data = $data;
        $this->key = 0;
    }

    /**
     * 返回当前元素
     */
    public function current()
    {
        // TODO: Implement current() method.
        return $this->data[$this->key];
    }

    /**
     * 前进到下一个元素
     */
    public function next()
    {
        // TODO: Implement next() method.
        return $this->key++;
    }

    /**
     * 返回当前元素的键
     */
    public function key()
    {
        // TODO: Implement key() method.
        return $this->key;
    }

    /**
     * 检查当前位置是否有效
     */
    public function valid()
    {
        // TODO: Implement valid() method.
        return isset($this->data[$this->key]);
    }

    /**
     * 将Iterator倒退到第一个元素
     */
    public function rewind()
    {
        // TODO: Implement rewind() method.
        return $this->key = 0;
    }
}

// 客户端调用
$concreteAggregate = new ConcreteAggregate();
$concreteAggregate->add('张三');
$concreteAggregate->add('李四');
$concreteAggregate->add('王五');

$concreteIterator = $concreteAggregate->getIterator();
foreach ($concreteIterator as $concrete) {
    echo $concrete . "<br>";
}

// 结果
张三
李四
王五