PHP 错误 : Fatal error: Constant expression contains invalid operations

Question

我收到一个错误:

Fatal error: Constant expression contains invalid operations in config.php on line 214

那一行是:

 protected static $dbname = 'mydb_'.$appdata['id'];

我是否在引号中犯了任何错误？还是其他地方？

我对错误消息的搜索仅显示了不同的来源(函数定义中的动态默认值)。

Answer 1

来自official Php documentation :

Like any other PHP static variable, static properties may only be initialized using a literal or constant before PHP 5.6; expressions are not allowed. In PHP 5.6 and later, the same rules apply as const expressions: some limited expressions are possible, provided they can be evaluated at compile time.

所以你不能用另一个变量初始化一个静态变量。将 $appdata['id'] 替换为常量字符串或删除 static 属性。

这是因为所有静态声明都在编译时解析，此时其他变量的内容未知(参见 this other page of official doc)。