Error in declaring multidimensional static PHP class array using static class arrays

Question

I'm refreshing my PHP knowledge and have a problem I can't solve on my own:

I have a class with two private static arrays that I want to store as values of a further (multideimensional) static class array but I always get a *unexpected T_VARIABLE* error. Here is my simplyfied sample code (just with one instead of two static arrays to fill in the following multidimensional array) that fails:

class MyClass {
  private static $firstArr = array('a' => 'A', 'b' => 'B');

  private static $multiArr = array('a' => self::$firstArr);
}

I really don't understand what's wrong here. I could easily replace the self::$firstArr with the array declaration of $firstArr itself, but I'd love to understand what I'm doing wrong here, anyway.

So any comment is welcome!

Cheers, Roman.

Mike B · Accepted Answer · 2012-08-12 13:56:43Z

3

You can't do any kind of extra evaluation when declaring class properties.

private static $multiArr = array('a' => self::$firstArr);
//                Can't do this    -----^

Link in docs

This declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

You're right to avoid copy/paste - This sort of 'run-time information' is usually done in the constructor.

edited Aug 12, 2012 at 13:56

answered Aug 12, 2012 at 13:49

Mike B

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2 Comments

RSeidelsohn Over a year ago

I see, sounds fair. Thank you for your explanation, I didn't know that yet (and it probably means that what I'm doing should better be done in a different way...).

darma Over a year ago

Yes it's a bit annoying, when you need to evaluate expressions from static properties you need to place those in a static init method that you call from the class file itself for example, or find another design.. @Mike B how do you manage that practically?

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