php - stdClass 动态成员 - 内存耗尽

Question

问题很简单:我有一个像

{a:'A', b:'B'}

我希望它像

{a:'A', new_a:'A', b:'B', new_b:'B'}

使用的代码是:

<?php

$obj = new stdClass();
$obj->a = 'A';
$obj->b = 'B';

foreach($obj as $field=>$value)
{
    $obj->{'new_'.$field} = $value;
}

输出是:

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 21290 bytes) in /path/to on line 9

第 9 行是这样的:

$obj->{'new_'.$field} = $value

我确实有解决问题的替代方案，但我不明白为什么这个特定代码会产生这个错误。有谁知道这个错误的原因，最终解释。谢谢!

Answer 1

问题是，当您迭代源对象属性时，您正在向源对象添加更多属性，因此 foreach 循环永远不会结束。

您可以通过向循环中添加一个 var_dump 调用来查看这种情况:

foreach ($obj as $field => $value)
{
    $obj->{'new_'.$field} = $value;
    var_dump($obj);
}

结果:

object(stdClass)#1 (29) {
  ["a"]=>
  string(1) "A"
  ["b"]=>
  string(1) "B"
  ["new_a"]=>
  string(1) "A"
  ["new_b"]=>
  string(1) "B"
  ["new_new_a"]=>
  string(1) "A"
  ["new_new_b"]=>
  string(1) "B"
  ["new_new_new_a"]=>
  ...

相反，创建一个新对象并替换旧对象:

$obj = new stdClass();
$obj->a = 'A';
$obj->b = 'B';

$newObj = new stdClass();

// Copy old properties
foreach ($obj as $field => $value) {
    $newObj->{$field} = $value;
}

// Create new properties
foreach($obj as $field => $value) {
    $newObj->{'new_' . $field} = $value;
}

甚至:

$obj = new stdClass();
$obj->a = 'A';
$obj->b = 'B';

$newObj = new stdClass();

// Copy old properties and create new
foreach ($obj as $field => $value) {
    $newObj->{$field} = $value;
    $newObj->{'new_' . $field} = $value;
}