PHP design pattern iterator pattern

Concept

Iterator mode (Iterator), also called Cursor (Cursor) mode. Provides a way to sequentially access the various elements in an aggregate object without exposing the object's internal representation.

When you need to access an aggregate object and need to traverse it no matter what these objects are, you should consider using the iterator pattern. In addition, when you need to traverse a collection in multiple ways, you can consider using the iterator pattern. The iterator pattern provides a unified interface for traversing different collection structures, such as the start, next, whether to end, and the current item.

Applicable scenarios

Access the contents of an aggregate object without exposing its internal representation

Supports multiple traversals of aggregate objects

Provides a unified interface for traversing different aggregate structures

UML diagram

Role

Iterator (iterator): Iterator defines the interface for accessing and traversing elements

ConcreteIterator (concrete iterator): A specific iterator implements the iterator interface and tracks the current position when traversing the aggregate

Aggregate (aggregation) : Aggregation defines the interface that creates the corresponding iterator object

ConcreteAggregate (concrete aggregation): The concrete aggregate implements the interface that creates the corresponding iterator. This operation returns an appropriate instance of ConcreteIterator

Code

The code is as follows:

PHP SPL The iterator interface Iterator and the container interface IteatorAggragate have been provided. The source code is as follows:

/**
 * Interface to detect if a class is traversable using &foreach;.
 * @link http://php.net/manual/en/class.traversable.php
 */
interface Traversable {
}

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

    /**
     * Retrieve an external iterator
     * @link http://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();
}

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

    /**
     * Return the current element
     * @link http://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 http://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 http://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 http://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 http://php.net/manual/en/iterator.rewind.php
     * @return void Any returned value is ignored.
     * @since 5.0.0
     */
    public function rewind();
}

Here we directly implement the above two interfaces, please see the following code:

<?php
header(&#39;Content-type:text/html;charset=utf-8&#39;);
/**
 * 迭代器模式
 */

/**
 * Class ConcreteIterator 具体的迭代器
 */
class ConcreteIterator implements Iterator
{
    private $position = 0;
    private $array = array();

    public function __construct($array) {
        $this->array = $array;
        $this->position = 0;
    }

    function rewind() {
        $this->position = 0;
    }

    function current() {
        return $this->array[$this->position];
    }

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

    function next() {
        ++$this->position;
    }

    function valid() {
        return isset($this->array[$this->position]);
    }
}

/**
 * Class MyAggregate 聚合容器
 */
class ConcreteAggregate implements IteratorAggregate
{
    public $property;

    /**
     * 添加属性
     *
     * @param $property
     */
    public function addProperty($property)
    {
        $this->property[] = $property;
    }

    public function getIterator()
    {
        return new ConcreteIterator($this->property);
    }
}

/**
 * Class Client 客户端测试
 */
class Client
{
    public static function test()
    {
        //创建一个容器
        $concreteAggregate = new ConcreteAggregate();
        // 添加属性
        $concreteAggregate->addProperty(&#39;属性1&#39;);
        // 添加属性
        $concreteAggregate->addProperty(&#39;属性2&#39;);
        //给容器创建迭代器
        $iterator = $concreteAggregate->getIterator();
        //遍历
        while($iterator->valid())
        {
            $key   = $iterator->key();
            $value = $iterator->current();
            echo &#39;键: &#39;.$key.&#39; 值: &#39;.$value.&#39;<hr>&#39;;
            $iterator->next();
        }

    }
}

Client:: test();

Running result:

Key: 0 Value: Attribute 1
Key: 1 Value: Attribute 2