为什么在类常量中指定一个定义的常量会引发错误？

Question

Here is part of my code

define('DIR_APP', 'app/');

 class Questions
    {


        const QUESTIONS_FILE = DIR_APP . 'questions.xml';
    }

Seems when I take the define()'d constant out of my class constant declaration, it works fine. But when I add it it throws this error:

Parse error: syntax error, unexpected '.', expecting ',' or ';' in /home/public_html/app/classes/Questions.class.php on line 7

So how can I get my define()'d constant in there? I assume it is not correctly looking up the DIR_APP thinking it might of been defined within the class. How do I get it to resolve it globally?

Thank you

Answer 1

It can't be done.

Quote from http://www.php.net/manual/en/language.oop5.constants.php :

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

I think you could

define('QUESTIONS_FILE', DIR_APP . 'questions.xml');

but that is global.