$userDatas = [
['user_id'=>1],
['user_id'=>3]
];
$userIds = [];
foreach ($userDatas as $item){
$userIds[] = $item['user_id'];
}
halt($userIds);
return $userIds;
输出:
array(2) {
[0] => int(1)
[1] => int(3)
} 如果将$userId[] 改为 $userId:
$userDatas = [
['user_id'=>1],
['user_id'=>3]
];
$userIds = [];
foreach ($userDatas as $item){
$userIds = $item['user_id'];
}
halt($userIds);
return $userIds;
输出:
int(3)
分析:去掉[],$userIds 视为变量,等于循环给变量赋值,第一次循环给变量赋值为1,第二次循环又给变量赋值为3,替换掉了1,所以输出:3