Public static variable value

Question

I'm trying to declare a public static variable that is a array of arrays:

class Foo{
 public static $contexts = array(
    'a' => array(
      'aa'              => something('aa'),
      'bb'              => something('bb'),
    ),

    'b' => array(
      'aa'              => something('aa'),
      'bb'              => something('bb'),
    ),

  );

 // methods here

 }

 function something($s){
   return ...
 }

But I get a error:

Parse error: parse error, expecting `')'' in ...

Solution

You can't use expressions when declaring class properties. I.e. you can't call something() here, you can only use static values. You'll have to set those values differently in code at some point.

Like any other PHP static variable, static properties may only be initialized using a literal or constant; expressions are not allowed. So while you may initialize a static property to an integer or array (for instance), you may not initialize it to another variable, to a function return value, or to an object.

http://www.php.net/manual/en/language.oop5.static.php

For example:

class Foo {
    public static $bar = null;

    public static function init() {
       self::$bar = array(...);
    }
}

Foo::init();

Or do it in __construct if you're going to instantiate the class.

Comments

[Alex]

that's weird, because I can just declare a public static function that will return my array, it would be the same

[Gromski]

The initial values of class properties are created while the source code is parsed. At that point memory needs to be reserved for those initial class values since they need to be stored somewhere. This happens before the code is actually executed. You can't reserve memory for the return value of a function though, since a function may return anything. And since parsing hasn't completed, functions can't be executed yet. Hence, while parsing the code, only static values of known size are allowed. A function is (explicitly) invoked later at runtime and may return anything.