How to extend static inherited array in PHP class

Question

Let's say I have a static array and I would like to add some more values into it in a child class. Since PHP does not have static constructor, I really don't know how to achieve this in a clean manner (I definitely don't want to add anything under the class definition and can't change the autoloader)

This is what I would like to achieve (obviously doesn't work)

class Parent{
    public static $meta = [1,2,3];
}

class Child extends Parent{
    public static $meta = array_merge(parent::$meta,[4,5]);

}

I'd recommend you to create singleton class that would share static information between classes you want. — Andy
– Andy, Commented Dec 29, 2017 at 16:46

Philipp · Accepted Answer · 2017-12-29 16:59:04Z

2

What you want isn't possible with vars inside classes. Instead I would suggest to provide the acccess to the var over an getter method. On top of this, I would suggest to make the static var protected, to prevent unwanted access from outside.

Using late static binding, you could provide a static function in the parent class, which merges the own var with the vars from the inherited class.

class A {
    protected static $meta = [1,2,3];

    public static function getMeta() {
        if (__CLASS__ == static::class) {
            return self::$meta;
        }
        return array_merge(self::$meta, static::$meta);
    }
}

class B extends A {
    protected static $meta = [4,5];
}

var_dump(B::getMeta());

The comparison of __CLASS__ == static::class is only needed for this example - if you go with assiciative arrays and just want to append new options, you could just ignore this and use a simple return self::$meta + static::$meta;

Keep in mind, this works only for one level inheritance. If you need a cascade of new $meta vars in the child classes, you have overwrite the getMeta method in the child classes too.

edited Dec 29, 2017 at 16:59

answered Dec 29, 2017 at 16:54

Philipp

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1 Comment

Unex Over a year ago

But calling A::getMeta() would return [1,2,3,1,2,3] which is a weird behavior

Unex · Accepted Answer · 2017-12-29 16:58:26Z

1

you are redefining an attribute in your child class which is not recommended. You can check here alternatives

Moreover parent is not an allowed name for a class. A solution would be to implement a static method wich return the property. Like this

class ParentClass{
    public static $meta = [1,2,3];

    public static function getMeta() {
        return self::$meta;
    }
}

class Child extends ParentClass{
    public static function getMeta() {
        return array_merge(parent::getMeta(),[4,5]);
    }
}

var_dump(Child::getMeta());

Result is

array(5) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
  [3]=>
  int(4)
  [4]=>
  int(5)
}

You can check this live here : https://3v4l.org/v8Mtm

Hope this help.

edited Dec 29, 2017 at 16:58

answered Dec 29, 2017 at 16:48

Unex

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Comments

Phillip Weber · Accepted Answer · 2017-12-29 18:01:29Z

The only way I can imagine doing this (without using a constructor or adding to the the class definition) is to use define consts like so;

/* FOO CLASS FILE */
define('FOO_META', [1, 2, 3]);

class Foo{
    public static $meta = FOO_META;
}

/* BAR CLASS FILE */
define('BAR_META', array_merge(FOO_META, [4, 5, 6]));

class Bar extends Foo{
    public static $meta = BAR_META;
}

echo 'Foo-Meta = ' . implode(', ', Foo::$meta) . '<br>';
echo 'Bar-Meta = ' . implode(', ', Bar::$meta) . '<br>';

Class properties can only be assigned const values inside the class definition. You will need to use a constructor (or some other method) to do this dynamically. If you use the above method, I would recommend using namespaces like so:

define('foo\META', [1, 2, 3]);
define('bar\META', array_merge(foo\META, [4, 5, 6]));

EDIT: if these classes consist only of this one property, why not just use the defines by themselves? They are essentially the same thing without the additional overhead.

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