类const的全局值

Question

Well, I have dealed with global and const values. Figure out something like this:

<?

global $foo;

class MyClass{

    const BAR = $foo;
...

Looks like this is not allowed, so I just want to know if is it valid code or is just a mistake in some assignation.

PS: I know that there are many ways to do what I am expecting, just want to discart this.

Answer 1

const expects a constant. $foo is a variable, not a constant.

It is clearly explained in the PHP Class Constant Documentation:

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