了解迭代器之前，先看看Iterator的接口，如下

Iterator extends Traversable {
abstract public mixed current ( void )//返回当前元素
abstract public scalar key( void )//返回当前元素的键
abstract public void next( void )//向前移动到下一个元素
abstract public void rewind( void )//返回到迭代器的第一个元素
abstract public boolean valid ( void )//检查当前位置是否有效
}

实例1

<?php
class MyIterator implements Iterator
{
    private $var = array();

    public function __construct($array)
    {
        if (is_array($array)) {
            $this->var = $array;
        }
    }

    public function rewind() {
        echo "rewinding<br/>";
        reset($this->var);
    }

    public function current() {
        $var = current($this->var);
        echo "current: $var<br/>";
        return $var;
    }

    public function key() {
        $var = key($this->var);
        echo "key: $var<br/>";
        return $var;
    }

    public function next() {
        $var = next($this->var);
        echo "next: $var<br/>";
        return $var;
    }

    public function valid() {
        $var = $this->current() !== false;
        
        echo "valid: {$var}<br/>";
        return $var;
    }
}

$values = array('name','age','sex');
$it = new MyIterator($values);


foreach ($it as $a => $b) {
    print "$a: $b<br/>";
    echo "<br/>";
    echo "<br/>";
    echo "<br/>";
}
?>

如下输出

Paste_Image.png

也可以用 IteratorAggregate(聚合式迭代器)来替代实现所有的 Iterator方法。IteratorAggregate 只需要实现一个方法 IteratorAggregate::getIterator()，其应返回一个实现了 Iterator的类的实例。

如下

<?php

class MyIterator implements Iterator
{
    private $var = array();

    public function __construct($array)
    {
        if (is_array($array)) {
            $this->var = $array;
        }
    }

    public function rewind() {
        echo "rewinding<br/>";
        reset($this->var);
    }

    public function current() {
        $var = current($this->var);
        echo "current: $var<br/>";
        return $var;
    }

    public function key() {
        $var = key($this->var);
        echo "key: $var<br/>";
        return $var;
    }

    public function next() {
        $var = next($this->var);
        echo "next: $var<br/>";
        return $var;
    }

    public function valid() {
        $var = $this->current() !== false;
        echo "valid: {$var}<br/>";
        return $var;
    }
}

class MyCollection implements IteratorAggregate
{
    private $items = array();
    private $count = 0;

   
    public function getIterator() {
        return new MyIterator($this->items);
    }

    public function add($value) {
        $this->items[$this->count++] = $value;
    }
}

$coll = new MyCollection();
$coll->add('value 1');
$coll->add('value 2');
$coll->add('value 3');

foreach ($coll as $key => $val) {
    echo "key/value: [$key -> $val]";
    echo "<br/>";
    echo "<br/>";
    echo "<br/>";
    echo "<br/>";
}
?>

如下输出

Paste_Image.png

实例2

<?php 
class myIterator implements Iterator {
    private $position = 0;
    private $array = array(
        "firstelement",
        "secondelement",
        "lastelement",
    );  

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

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

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

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

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

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

$it = new myIterator;

foreach($it as $key => $value) {
    var_dump($key, $value);
    echo "<br/>";
}

?>

如下输出

Paste_Image.png