PHP 错误：致命错误：常量表达式包含无效操作
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PHP Error : Fatal error: Constant expression contains invalid operations
提问by Raja Gopal
I am getting an error:
我收到一个错误：
Fatal error: Constant expression contains invalid operations in config.php on line 214
致命错误：常量表达式在第 214 行的 config.php 中包含无效操作
That line was:
那一行是：
protected static $dbname = 'mydb_'.$appdata['id'];
Whether I did any mistakes in quotes? Or somewhere else?
我在引号中是否有任何错误？或者别的地方？
My search for the error message only showed a different source cause (a dynamic default value in a function definition).
我对错误消息的搜索只显示了不同的源原因（函数定义中的动态默认值）。
采纳答案by Al Foиce ?
From the official Php documentation:
来自官方 PHP 文档：
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.
与任何其他 PHP 静态变量一样，在 PHP 5.6 之前，静态属性只能使用文字或常量进行初始化；不允许使用表达式。在 PHP 5.6 及更高版本中，适用于 const 表达式的相同规则：一些有限的表达式是可能的，前提是它们可以在编译时计算。
So you cannot initialize a static variable with another variable. Replace $appdata['id']with a constant string or remove the staticattribute.
所以你不能用另一个变量初始化一个静态变量。替换$appdata['id']为常量字符串或删除该static属性。
This is because all static declarations are resolved in compile-time, when the content of other variables is not known (see this other page of official doc).
这是因为所有静态声明都在编译时解析，当其他变量的内容未知时（请参阅官方文档的其他页面）。
回答by álvaro González
Unless you mess with reflection, the only way I can think of to have a static private/protected class property with a dynamically generated value is to calculate it outside the class:
除非你弄乱了反射，否则我能想到的唯一方法是拥有一个动态生成的值的静态私有/受保护的类属性是在类之外计算它：
class Foo {
protected static $dbname = DBNAME;
public static function debug() {
return Foo::$dbname;
}
}
$appdata = array(
'id' => 31416,
);
define('DBNAME', 'mydb_'.$appdata['id']);
var_dump(Foo::debug());
In your precise use case, however, it's possiblethat there's simply no good reason for the property to be static. In that case, it's as straightforward as using the constructor:
但是，在您的精确用例中，该属性可能根本没有充分的理由是静态的。在这种情况下，就像使用构造函数一样简单：
class Foo {
protected $dbname;
public function __construct($appdata){
$this->dbname = 'mydb_'.$appdata['id'];
}
public function debug() {
return $this->dbname;
}
}
$appdata = array(
'id' => 31416,
);
$foo = new Foo($appdata);
var_dump($foo->debug());
回答by Mayank Pandeyz
Raja this is because a static variable contains a constant value in it. But in your case:
Raja 这是因为静态变量中包含一个常量值。但在你的情况下：
protected static $dbname = 'mydb_'.$appdata['id'];
$appdata['id']is dynamic that can change its value during the execution. That's why the error is showing.
$appdata['id']是动态的，可以在执行期间更改其值。这就是错误显示的原因。
回答by Hyman
I had this error and my fix was to not declare a date within a class property array
我遇到了这个错误，我的解决方法是不在类属性数组中声明日期
public static $config_array = array(
'start_date' => date('Y-m-d H:i:s') // No can do
);
