php 生成器 yield 实现的递归

原始递归方法：

<?php
echo "<pre>";
$area = array(
array('id'=>1,'area'=>'北京','pid'=>0),
array('id'=>2,'area'=>'广西','pid'=>0),
array('id'=>3,'area'=>'广东','pid'=>0),
array('id'=>4,'area'=>'福建','pid'=>0),
array('id'=>11,'area'=>'朝阳区','pid'=>1),
array('id'=>12,'area'=>'海淀区','pid'=>1),
array('id'=>21,'area'=>'南宁市','pid'=>2),
array('id'=>45,'area'=>'福州市','pid'=>4),
array('id'=>113,'area'=>'亚运村','pid'=>11),
array('id'=>115,'area'=>'奥运村','pid'=>11),
array('id'=>234,'area'=>'武鸣县','pid'=>21)
);

function t($arr,$pid=0,$lev=0){
static $list = array();
foreach($arr as $v){
if($v['pid']==$pid){
echo str_repeat(" ",$lev).$v['area']."<br />";
//这里输出，是为了看效果
$list[] = $v;
t($arr,$v['id'],$lev+1);
}
}
return $list;
}
$list = t($area);
echo "<hr >";
print_r($list);
?>

用　yield 实现

<?php
echo "<pre>";
$area = array(
array('id'=>1,'area'=>'北京','pid'=>0),
array('id'=>2,'area'=>'广西','pid'=>0),
array('id'=>3,'area'=>'广东','pid'=>0),
array('id'=>4,'area'=>'福建','pid'=>0),
array('id'=>11,'area'=>'朝阳区','pid'=>1),
array('id'=>12,'area'=>'海淀区','pid'=>1),
array('id'=>21,'area'=>'南宁市','pid'=>2),
array('id'=>45,'area'=>'福州市','pid'=>4),
array('id'=>113,'area'=>'亚运村','pid'=>11),
array('id'=>115,'area'=>'奥运村','pid'=>11),
array('id'=>234,'area'=>'武鸣县','pid'=>21)
);

function t($arr,$pid=0,$lev=0){
static $list = array();
foreach($arr as $v){
if($v['pid']==$pid){
echo str_repeat(" ",$lev).$v['area']."<br />";
//这里输出，是为了看效果
$list[] = $v;
foreach(t($arr,$v['id'],$lev+1) as $value){
yield $value;
}
}
}
yield $list;
}

foreach (t($area) as $key => $value) {
$list=$value;
}
echo "<hr >";
print_r($list);

?>