SPL学习 迭代器

//内部不使用数组，实现迭代器
class Fibonacci implements Iterator { 
    private $previous = 0; 
    private $current = 1; 
    private $key = 0; 
    
    public function current() { 
        return $this->current; 
    } 
    
    public function key() { 
        return $this->key; 
    } 
    
    public function next() { 
        // 关键在这里
        // 将当前值保存到  $newprevious
        $newprevious = $this->current; 
        // 将上一个值与当前值的和赋给当前值
        $this->current += $this->previous; 
        // 前一个当前值赋给上一个值
        $this->previous = $newprevious; 
        $this->key++; 
    } 
    
    public function rewind() { 
        $this->previous = 1; 
        $this->current = 0; 
        $this->key = 0; 
    } 
    
    public function valid() { 
        if($this->key>12) return false;
        return true; 
    } 
} 

//内部用数组构建一个迭代器，同时实现了 数组式访问，随即跳转，count计数
class arrFibonacci implements Iterator, ArrayAccess, SeekableIterator, Countable{ 
    private $arr = array(0,1);    
    private $pos = 0;
    
    //循环 Iterator
    public function current() { 
        return $this->arr[$this->pos];
    } 
    
    public function key() { 
        return $this->pos;
    } 
    
    public function next() { 
        $this->pos++;
        if($this->pos > 1 && !isset($this->arr[$this->pos]) ){
            $this->arr[$this->pos] =  $this->arr[$this->pos-2] + $this->arr[$this->pos-1];
        }        
    } 
    
    public function rewind() { 
        $this->pos = 0;
    } 
    
    public function valid() { 
        if($this->pos>=15) return false;
        return isset($this->arr[$this->pos]);
    } 
    
    //数组式访问元素 ArrayAccess
    function offsetExists($offset) {
        return isset($this->arr[$offset]);
    }    
    
    function offsetGet($offset){
        return $this->arr[$offset];
    }
    
    function offsetSet($offset, $value){
        if(isset($this->arr[$offset]))
            $this->arr[$offset] = $value;
    }
    
    function offsetUnset($offset){
        unset( $this->arr[$offset] );
    }

    //跳转 SeekableIterator
    function seek($position) {
        echo $position,‘<br>‘;
        if ( isset($this->arr[$position]) ) {
            $this->pos = $position;
        }
    }
    
    //计数
    function count(){
        return count( $this->arr );
    }

    //显示，为了验证，不需要对应SPL接口
    public function show(){
        showarr($this->arr);
    }
} 

// ArrayAccess 让一个类具有数组式访问模式
class Article implements ArrayAccess { 
    public $title;
    public $author;
    public $category;  

    function __construct($title,$author,$category) {
        $this->title = $title;
        $this->author = $author;
        $this->category = $category;
    }

    function offsetExists($key) {
        return array_key_exists($key,get_object_vars($this)); //get_object_vars — 返回由对象属性组成的关联数组
    }
    
    function offsetSet($key, $value) {
        if ( array_key_exists($key,get_object_vars($this)) ) {
         $this->{$key} = $value;
        }
    }

    function offsetGet($key) {
        if ( array_key_exists($key,get_object_vars($this)) ) {
         return $this->{$key};
        }
    }

    function offsetUnset($key) {
        if ( array_key_exists($key,get_object_vars($this)) ) {
         unset($this->{$key});
        }
    }

}

// 让一个类 返回一个迭代器
class arrArticle implements IteratorAggregate {
    public $arr = array();

    function __construct($title,$author,$category) {
        $this->arr[‘title‘] = $title;
        $this->arr[‘author‘] = $author;
        $this->arr[‘category‘] = $category;
    }

    //可以用 IteratorAggregate 接口 返回一个 Iterator
    function getIterator() {
        return new ArrayIterator( $this->arr );
    }

}