【SPL标准库专题(2)】Iterator

摘要：由于没有方法，所以就不能用重置游标，这个时候已经到最后了，所以为空一种占位符形式的迭代器，不执行任何操作。检查是否含有子节点输出所有字节点将一个树形结构的迭代器展开为一维结构。

本段内容来自阮一峰老师再加自己的部分注解

SPL规定，所有部署了Iterator界面的class，都可以用在foreach Loop中。Iterator界面中包含5个必须部署的方法：

* current()

This method returns the current index"s value. You are solely
responsible for tracking what the current index is as the 
interface does not do this for you. (返回当前索引值)

* key()

This method returns the value of the current index"s key. For 
foreach loops this is extremely important so that the key 
value can be populated. (返回当前的索引key)

* next()

This method moves the internal index forward one entry. (迭代中的内部指针往前进一步)

* rewind()

This method should reset the internal index to the first element. (重置迭代中的内部指针)

* valid()

This method should return true or false if there is a current 
element. It is called after rewind() or next(). (验证内部指针是否到最后一行)

Example

class ArrayReloaded implements Iterator {
  /**
   * 如前一篇文章所说,该类实现了Iterator接口,所以该类对象就是ZEND_ITER_OBJECT,对于ZEND_ITER_OBJECT的类对象,会通过调用对象实现的Iterator接口相关函数来进行foreach。
   */
  private $array = array();
  private $valid = FALSE;

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

  function rewind(){
    /**
     *  reset: 将数组的内部指针指向第一个单元,如果数组为空则返回false;
     *  所以下述语句表示: 数组不为空并且已重置到第一个单元;
     */
    $this->valid = (FALSE !== reset($this->array));
  }

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

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

  function next(){
    /**
     * next: 将数组中的内部指针向前移动一位
     * 返回数组内部指针指向的下一个单元的值，或当没有更多单元时返回 FALSE。
     * 所以下述语句表示: 如果还有下一个单元的话,指针移动到下个单元并返回true;
     */
    $this->valid = (FALSE !== next($this->array));
  }

  function valid(){
    return $this->valid;
  }

  #↑↑ 以上5个方法是必须实现的接口方法,也可以再扩展prev和end等方法,后续会介绍一些SPL内置的实现了itertor接口的类,这些类可以拿来直接使用
}

$arr = array(
  "color1" => "red",
  "color2" => "blue",
  "color3" => "green",
  "color4" => "plack",
  "color5" => "purple"
);

$colors = new ArrayReloaded($arr);

# 通过foreach来遍历
foreach($colors as $k => $v){
  echo $k.":".$v."
";
}

# 通过while来遍历
/**
 * 1: foreach的内部实现方式其实也是如此,事实上直接用while来遍历性能更高
 * 2: 在使用迭代器来遍历的时候,一定要记住要rewind和next,而PHP的foreach遍历早已把rewind和next给集成了;
 */
echo "
";
$colors -> rewind();
while($colors -> valid()){
  echo $colors -> key().":".$colors -> current()."
";
  $colors -> next();
}

ArrayIterator implements ArrayAccess , SeekableIterator , Countable , Serializable

这是一个非常有用的迭代器,里面实现了排序,添加,筛选等foreach不能直接实现的方法(都是要全部遍历出来再进行判断处理,代码不优雅维护性差)

Example

 "red",
  "color3" => "green",
  "color4" => "plack",
  "color2" => "blue",
  "color5" => "purple"
);

// $colors = new ArrayIterator($arr); //可以直接通过实例一个数组迭代器对象,然后while这个迭代器;

//但以下的方式要更易于扩展
//先实例一个array对象
$colorsObj = new ArrayObject($arr);
$it = $colorsObj -> getIterator(); //获得当前的ArrayIterator

# 通过while来遍历
$it -> rewind();
while($it -> valid()){
  echo $it -> key().":".$it -> current()."
";
  $it -> next();
}

#通过iterator迭代器来遍历就变得很灵活
echo $colorsObj -> count(); //元素数量统计

//从第三个开始遍历
$it -> rewind(); //凡是要使用迭代器之前先重置;
if($it -> valid()){
  $it -> seek(2); //从0开始的,第二个位置
  while($it -> valid()){
    echo $it -> key().":".$it -> current()."
";
    $it -> next();
  }
}

//对索引名进行升序排列
$it -> ksort();
foreach($it as $k => $v){
  echo $k ."-->". $v."
";
}

//对索引值进行排序
$it -> asort();
foreach($it as $k => $v){
  echo $k ."-->". $v."
";
}

//这些对象方法是否很熟悉? 这就是上一篇文章中说到的 "SPL是一种使object（物体）模仿array（数组）行为的interfaces和classes"

按顺序迭代访问几个不同的迭代器。例如，希望在一次循环中迭代访问两个或者更多的组合。这个迭代器的append方法类似于array_merge()函数来合并数组。

Example

$arr1 = array(
  "color1" => "red",
  "color3" => "green",
  "color4" => "plack",
  "color2" => "blue",
  "color5" => "purple"
);

$arr2 = array(
  "fruit1" => "apple",
  "fruit2" => "orange",
  "fruit3" => "banana",
  "fruit4" => "grape",
  "fruit5" => "strawberry",
);

$ao1 = new ArrayIterator($arr1);
$ao2 = new ArrayIterator($arr2);
$iterator = new AppendIterator();
$iterator -> append($ao1);
$iterator -> append($ao2);
foreach($iterator as $k => $v){
  echo $k.":".$v,"
";
}

迭代器的链接器，更多参考连接 http://php.net/manual/en/clas...

$person_id = new ArrayIterator(array("001", "002", "003")); 
$person_name = new ArrayIterator(array("张三", "李四", "王五")); 
$person_age = new ArrayIterator(array(22, 23, 11)); 
$mit = new MultipleIterator(MultipleIterator::MIT_KEYS_ASSOC); 
$mit->attachIterator($person_id, "ID"); 
$mit->attachIterator($person_name, "NAME"); 
$mit->attachIterator($person_age, "AGE"); 
echo"连接的迭代器个数:".$mit->countIterators() . "
"; //3 
foreach ($mit as $person) { 
    print_r($person); 
} 
/**output
Array
(
    [ID] => 001
    [NAME] => 张三
    [AGE] => 22
)
Array
(
    [ID] => 002
    [NAME] => 李四
    [AGE] => 23
)
Array
(
    [ID] => 003
    [NAME] => 王五
    [AGE] => 11
)
**/ 

返回给定数量的结果以及从集合中取出结果的起始索引点

FilterIterator
基于OuterIterator接口，用于过滤数据，返回符合条件的元素。必须实现一个抽象方法accept()，此方法必须为迭代器的当前项返回true或false
class UserFilter extends FilterIterator{
  private $userFilter;

  public function  __construct(Iterator $iterator , $filter){
    parent::__construct($iterator);
    //要过滤的参数
    $this->userFilter = $filter;
  }

  public function accept(){
    /*
     * getInnerIterator(): 获得内部的迭代器
     * current(): 然后获取当前的元素
     * in strcmp(string str1,string str2) 区分字符串中字母大小写地比较,返回0就相同
     * int strcasecmp(string str1,string str2) 忽略字符串中字母大小写地比较，返回0就相同
     * 如果accept返回false的话就过滤掉
     */
    $user = $this->getInnerIterator()->current();
    if (strcasecmp($user["name"] , $this->userFilter) == 0) {
      return false;
    }
    return true;
  }
}

$array = array (array ("name" => "Jonathan" , "id" => "5") , array ("name" => "Abdul" , "id" => "22"),array ("name" => "zhouzhou" , "id" => "9"));
$object = new ArrayObject($array);
//去除掉名为abdul的人员
$iterator = new UserFilter($object->getIterator() , "abdul");
foreach ($iterator as $result) {
  echo $result["name"];
}

/**output
 * Jonathan
 **/
RegexIterator
继承FilterIterator，支持使用正则表达式模式匹配和修改迭代器中的元素。经常用于将字符串匹配。
更多参考： http://cn2.php.net/manual/zh/...
//可以实现:  preg_match_all(), preg_match(), preg_replace(),preg_split()等函数的功能

$a = new ArrayIterator(array("test1", "test2", "test3"));
$i = new RegexIterator($a, "/^(test)(d+)/", RegexIterator::REPLACE);
$i->replacement = "$2:$1";
print_r(iterator_to_array($i));

/**output
Array
(
[0] => 1:test
[1] => 2:test
[2] => 3:test
)
 **/
IteratorIterator
一种通用类型的迭代器，所有实现了Traversable接口的类都可以被它迭代访问。
CachingIterator
用来执行提前读取一个元素的迭代操作，例如可以用于确定当前元素是否为最后一个元素。
$array = array ("koala" , "kangaroo" , "wombat" , "wallaby" , "emu" , "kiwi" , "kookaburra" , "platypus");
$object = new CachingIterator(new ArrayIterator($array));
foreach ($object as $value) {
  echo $value;
  if ($object->hasNext()) {
    echo ","; //如果有下一项的话才输出 突出不了该迭代器的作用啊，其他迭代器也可以搞定的
  }
}
/**output
 * koala,kangaroo,wombat,wallaby,emu,kiwi,kookaburra,platypus
 **/
SeekableIterator
用于创建非顺序访问的迭代器，允许跳转到迭代器中的任何一点上。
$array = array("apple", "banana", "cherry", "damson", "elderberry");
$iterator = new ArrayIterator($array);
$iterator->seek(3); //起始0从第3个开始取；
echo $iterator->current()."
";
/**output
damson
 **/
NoRewindIterator
用于不能多次迭代的集合，适用于在迭代过程中执行一次性操作。
$fruit = array("apple", "banana", "cranberry");
$arr = new ArrayObject($fruit);
$it = new NoRewindIterator($arr->getIterator());
echo "Fruit A:
";
foreach ($it as $item) {
  echo $item . "
";
}

echo "Fruit B:
"; 

// ↓↓ 由于NoRewindIterator没有rewind方法，所以foreach就不能用rewind重置游标，这个时候$it已经到最后了，所以为空；
foreach ($it as $item) {
  echo $item . "
";
}

/**output
Fruit A:
apple
banana
cranberry
Fruit B:
 **/
EmptyIterator
一种占位符形式的迭代器，不执行任何操作。当要实现某个抽象类的方法并且这个方法需要返回一个迭代器时，可以使用这种迭代器。
InfiniteIterator
用于持续地访问数据，当迭代到最后一个元素时，会再次从第一个元素开始迭代访问。
$arrayit = new ArrayIterator(array("cat", "dog"));
$infinite = new InfiniteIterator($arrayit);

//必须限制否则就是死循环
$limit = new LimitIterator($infinite, 0, 7);
foreach ($limit as $value) {
  echo "$value
";
}
RecursiveArrayIterator
创建一个用于递归形式数组结构的迭代器，类似于多维数组.它为许多更复杂的迭代器提供了所需的操作，如RecursiveTreeIterator和RecursiveIteratorIterator迭代器。
$fruits = array("a" => "lemon", "b" => "orange", array("a" => "apple", "p" => "pear"));
$iterator = new RecursiveArrayIterator($fruits);
while ($iterator->valid()) {
  //检查是否含有子节点
  if ($iterator->hasChildren()) {
    //输出所有字节点
    foreach ($iterator->getChildren() as $key => $value) {
      echo $key . " : " . $value . "
";
    }
  } else {
    echo "No children.
";
  }
  $iterator->next();
}

/**output
No children.
No children.
a : apple
p : pear
 **/
RecursiveIteratorIterator
将一个树形结构的迭代器展开为一维结构。
$fruits = array("a" => "lemon", "b" => "orange", array("a" => "apple", "p" => "pear","c" => ["a","b"]));
$arrayiter = new RecursiveArrayIterator($fruits);
$iteriter = new RecursiveIteratorIterator($arrayiter);
foreach ($iteriter as $key => $value) {
  $d = $iteriter->getDepth();
  echo "depth=$d k=$key v=$value
";
}
/**output
depth=0 k=a v=lemon
depth=0 k=b v=orange
depth=1 k=a v=apple
depth=1 k=p v=pear
depth=2 k=0 v=a
depth=2 k=1 v=b
 **/
RecursiveTreeIterator
以可视在方式显示一个树形结构。
$hey = array("a" => "lemon", "b" => "orange", array("a" => "apple", "p" => "pear"));
$awesome = new RecursiveTreeIterator(
  new RecursiveArrayIterator($hey),
  null, null, RecursiveIteratorIterator::LEAVES_ONLY
);
foreach ($awesome as $line)
  echo $line . PHP_EOL;

/**output
|-lemon
|-orange
  |-apple
  -pear
 **/
ParentIterator
是一个扩展的FilterIterator迭代器，它可以过滤掉来自于RecursiveIterator迭代器的非父元素，只找出子节点的键值。通俗来说，就是去枝留叶。
$hey = array ("a" => "lemon" , "b" => "orange" , array ("a" => "apple" , "p" => "pear"));
$arrayIterator = new RecursiveArrayIterator($hey);
$it = new ParentIterator($arrayIterator);
print_r(iterator_to_array($it));
/**output
 * Array
 * (
 * [0] => Array
 * (
 * [a] => apple
 * [p] => pear
 * )
 * )
 **/
RecursiveFilterIterator
是FilterIterator迭代器的递归形式，也要求实现抽象的accept()方法，但在这个方法中应该使用$this->getInnerIterator()方法访问当前正在迭代的迭代器。
class TestsOnlyFilter extends RecursiveFilterIterator{
  public function accept(){
    // 找出含有“叶”的元素
    return $this->hasChildren() || (mb_strpos($this->current() , "叶") !== false);
  }
}

$array = array ("叶1" , array ("力2" , "叶3" , "叶4") , "叶5");
$iterator = new RecursiveArrayIterator($array);
$filter = new TestsOnlyFilter($iterator);
$filter = new RecursiveIteratorIterator($filter);
print_r(iterator_to_array($filter));
/**output
 * Array
 * (
 * [0] => 叶1
 * [1] => 叶3 //只会找出含叶的元素，不会把元素成员全部显示出来
 * [2] => 叶5
 * )
 **/
RecursiveRegexIterator
是RegexIterator迭代器的递归形式，只接受RecursiveIterator迭代器作为迭代对象。
$rArrayIterator = new RecursiveArrayIterator(array ("叶1" , array ("tet3" , "叶4" , "叶5")));
$rRegexIterator = new RecursiveRegexIterator(
  $rArrayIterator , "/^叶/" , RecursiveRegexIterator::ALL_MATCHES
);
foreach ($rRegexIterator as $key1 => $value1) {
  if ($rRegexIterator->hasChildren()) {
    // print all children
    echo "Children: ";
    foreach ($rRegexIterator->getChildren() as $key => $value) {
      echo $value . " ";
    }
    echo "
";
  } else {
    echo "No children
";
  }
}
/**output
 * No children
 * Children: 叶4 叶5
 **/
RecursiveCachingIterator
在RecursiveIterator迭代器上执行提前读取一个元素的递归操作。
CallbackFilterIterator(PHP5.4)
同时执行过滤和回调操作，在找到一个匹配的元素之后会调用回调函数。
$hey = array ("李1" , "叶2" , "叶3" , "叶4" , "叶5" , "叶6" ,);
$arrayIterator = new RecursiveArrayIterator($hey);

$isYe = function($current){
  return mb_strpos($current , "叶") !== false;
};

$rs = new CallbackFilterIterator($arrayIterator , $isYe);
print_r(iterator_to_array($rs));

/**output
 * Array
 * (
 * [0] => 叶2
 * [1] => 叶3
 * [2] => 叶4
 * [3] => 叶5
 * [4] => 叶6
 * )
 **/
RecursiveCallbackFilterIterator(PHP5.4)
在RecursiveIterator迭代器上进行递归操作，同时执行过滤和回调操作，在找到一个匹配的元素之后会调用回调函数。
function doesntStartWithLetterT($current){
  $rs = $current->getFileName();
  return $rs[0] !== "T";
}

$rdi = new RecursiveDirectoryIterator(__DIR__);
$files = new RecursiveCallbackFilterIterator($rdi , "doesntStartWithLetterT");
foreach (new RecursiveIteratorIterator($files) as $file) {
  echo $file->getPathname() . PHP_EOL;
}

DirectoryIterator
目录文件遍历器，提供了查询当前文件的所有信息的方法（是否可读可写，所属，权限等等），具体参考 http://cn2.php.net/manual/zh/...
$it = new DirectoryIterator("../");
foreach ($it as $file) {
  //用isDot ()方法分别过滤掉“.”和“..”目录
  if (!$it->isDot()) {
    echo $file . "
";
  }
}

RecursiveDirectoryIterator
递归目录文件遍历器，可实现列出所有目录层次结构，而不是只操作一个目录。具体看：http://cn2.php.net/manual/zh/...
//列出指定目录中所有文件
$path = realpath("../");
$objects = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($path) , RecursiveIteratorIterator::SELF_FIRST);
foreach ($objects as $name => $object) {
  echo "$name
";
}
FilesystemIterator
是DirectoryIterator的遍历器
$it = new FilesystemIterator("../");
foreach ($it as $fileinfo) {
  echo $fileinfo->getFilename() . "
";
}

GlobIterator
带匹配模式的文件遍历器
$iterator = new GlobIterator("*.php");
if (!$iterator->count()) {
  echo "无php文件";
} else {
  $n = 0;
  printf("总计 %d 个php文件
" , $iterator->count());
  foreach ($iterator as $item) {
    printf("[%d] %s
" , ++ $n , $iterator->key());
  }
}
SimpleXMLIterator
XMl文档访问迭代器，可实现访问xml中所有节点
$xml = <<
        
            
            Jim Smith
        
        XML basics

XML;
// SimpleXML转换为数组
function sxiToArray($sxi){
  $a = array ();
  for ($sxi->rewind();$sxi->valid();$sxi->next()) {
    if (!array_key_exists($sxi->key() , $a)) {
      $a[$sxi->key()] = array ();
    }
    if ($sxi->hasChildren()) {
      $a[$sxi->key()][] = sxiToArray($sxi->current());
    } else {
      $a[$sxi->key()][] = strval($sxi->current());
    }
  }
  return $a;
}

$xmlIterator = new SimpleXMLIterator($xml);
$rs = sxiToArray($xmlIterator);
print_r($rs);
/**output
 * Array
 * (
 * [book] => Array
 * (
 * [0] => Array
 * (
 * [title] => Array
 * (
 * [0] => PHP Basics
 * )
 * [author] => Array
 * (
 * [0] => Jim Smith
 * )
 * )
 * [1] => XML basics
 * )
 * )
 **/
参考链接：
http://www.ruanyifeng.com/blo...
http://www.cnblogs.com/Script...