PHP: Extending static member arrays

Question

I'm having the following scenario:

class A { public static $arr=array(1,2); }
class B extends A { public static $arr=array(3,4); }

Is there any way to combine these 2 arrays so B::$arr is 1,2,3,4?

I don't need to alter these arrays, but I can't declare them als const, as PHP doesn't allow const arrays.http://stackoverflow.com/questions/ask The PHP manual states, that I can only assign strings and constants, so parent::$arr + array(1,2) won't work, but I think it should be possible to do this.

Answer 1

You're correct, you can only assign literals and constants when declaring a static variable. The work-around would be to assign the value in code just after the class is declared. In Java you could do this nicely with a static initialiser, but PHP doesn't support those either, so we have to define and call a method ourselves:

class A { public static $arr=array(1,2); }
class B extends A {
  public static $arr;
  public static function init() {
    self::$arr = array_merge(parent::$arr, array(3,4));
  }
}; B::init();

Also note the use of array_merge instead of the union (+) operator - the union operator won't combine the arrays as you intend, as they have identical numerical keys - the first is array(0=>1, 1=>2), second is array(0=>3, 1=>4); the union of them will only contain each key once, so you'll either end up with (1,2) or (3,4) depending on the order you union them.

Answer 2

Yes, you just need to get a bit fancy as you won't be able to define a static variable.

<?php

class A 
{
    public static $arr = array(1, 2);
    public static function getArr(){ return self::$arr; }
}

class B extends A 
{
    public static $arr = array(3, 4);
    public static function getArr(){ return array_merge(parent::$arr, self::$arr); }
}


print_r( A::getArr() );
print_r( B::getArr() );

Output:

Array
(
    [0] => 1
    [1] => 2
)
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
)

Also good since you can access the original arrays too:

print_r( A::$arr );
print_r( B::$arr );

Array
(
    [0] => 1
    [1] => 2
)
Array
(
    [0] => 3
    [1] => 4
)