php常量数学运算

Question

目前我正在学习php。我很困惑这是我的 php 代码

class OBJECT_ENUM
{
    const USER = 10;
    const POST = 30;
    const SECURE_REQUEST = 40;
}

class OPERATION_ENUM
{
    const INSERT_USER = OBJECT_ENUM::USER + 1; // <- here it gives an error
    const SEND_MAIL = OBJECT_ENUM::USER + 2;

    const LIKE_POST = OBJECT_ENUM::POST + 1;
    const INSERT_POST = OBJECT_ENUM::POST + 2;

    const ENCRYPT = OBJECT_ENUM::SECURE_REQUEST + 1;
}

error message: 
Parse error: syntax error, unexpected '+', expecting ',' or ';' in /var/www/workspace/6thAssignment/include/tempCall.php on line 15

我只是不明白为什么会发生这个错误。？有人能给我解释一下吗？？

提前谢谢

Answer 1

原始答案:

正如您在 http://www.php.net/manual/en/language.oop5.constants.php 中看到的那样:

The value must be a constant expression, not (for example) a variable, a property, a result of a mathematical operation, or a function call.

更新:

从 PHP 版本 5.6 now it is possible to use expressions为常数。