24php中使用Iterator，ArrayAccess和Countable

<?php
class Basket implements Iterator{
    private $fruits = array('apple', 'banna', 'pear', 'orange', 'watermelon');
    private $position = 0; 
    
    //返回当前的元素
    public function current(){
        return $this->fruits[$this->position];
    }
    //返回当前的键
    public function key(){
        return $this->position
    }
    //下移一个元素
    public function next(){
        ++$this->position;
    }
    
    //移动到第一个元素
    public function rewind(){
        $this->position = 0;
    }
    //判断后续是否还有元素
    public function valid(){
        return isset($this->fruits[$this->position+1]);
    }
    
}

<?php
class obj implements ArrayAccess{
    private $container = array();

    public function __construct(){
        $this->container = array(
            "one" => 1,
            "two" => 2,
            "three" => 3
            
        );
    }
    
    //赋值
    public function offsetSet($offset, $value){
        if(is_null($offset)){
            $this->container[] = $value;
        } else {
            $this->container[$offset] = $value;
        }
    }
    
    //某键是否存在
    public function offsetExists($offset){
        return isset($this->container[$offset]);
    }
    
    //删除键值
    public function offsetUnset($offset){
        unset($this->container[$offset]);
    }
    
    //获取键对应的值
    public function offsetGet($offset){
        return isset($this->container[$offset])?$this->container[$offset]:null;
    }
}

$obj = new obj();
var_dump(isset($obj["two"]));
var_dump($obj["two"]);
unset($obj["two"]);
var_dump(isset($obj["two"]));
$obj['two'] = "A value";

var_dump($obj['two']);
echo $obj['two'];
$obj[] = 'Append 1';
$obj[] = 'Append 2';
$obj[] = 'Append 3';
var_dump($obj);

<?php 
class Basket implements Countable{
    private $fruits = array('apple', 'banna', 'pear', 'orange', 'watermelon');
    public function count(){
        return count($this->fruits);
    }
}

$basket = new Basket();
echo count($basket);