php数组使用引用遍历多次时出现最后一个元素丢失问题

1、问题

$list = [
    ['id'=>1, 'name'=>'不知火舞', 'location'=>'中单'],
    ['id'=>2, 'name'=>'橘右京', 'location'=>'打野'],
    ['id'=>3, 'name'=>'马可波罗', 'location'=>'ADC'],
];

foreach ($list as &$item){
    $item['class'] = '刺客';
}

$list2 = [];
foreach ($list as $item){
    $list2[] = $item;
}

var_dump($list2);

/*
--$list2
array:3 [
  0 => array:4 ["id" => 1, "name" => "不知火舞", "location" => "中单", "class" => "刺客"]
  1 => array:4 ["id" => 2, "name" => "橘右京", "location" => "打野", "class" => "刺客"]
  2 => array:4 ["id" => 2, "name" => "橘右京", "location" => "打野", "class" => "刺客"]
]
*/

2、原因

原来是因为在遍历时使用引用，当第二次遍历数组时，数组的指针 $item
还是指向数组的末尾的元素，当重新赋值时 $item 指向的数组的末尾的元素就被修改了
解决办法是在第一次遍历完成之后就将$item unset()掉。

3、解决

$list = [
    ['id'=>1, 'name'=>'不知火舞', 'location'=>'中单'],
    ['id'=>2, 'name'=>'橘右京', 'location'=>'打野'],
    ['id'=>3, 'name'=>'马可波罗', 'location'=>'ADC'],
];

foreach ($list as &$item){
    $item['class'] = '刺客';
}
unset($item);//第一次遍历完成之后就将$item销毁

$list2 = [];
foreach ($list as $item){
    $list2[] = $item;
}

var_dump($list2);

/*
--$list2
array:3 [
  0 => array:4 ["id" => 1, "name" => "不知火舞", "location" => "中单", "class" => "刺客"]
  1 => array:4 ["id" => 2, "name" => "橘右京", "location" => "打野", "class" => "刺客"]
  2 => array:4 ["id" => 3, "name" => "马可波罗", "location" => "ADC", "class" => "刺客"]
]
*/