Merge array property of descendant objects

Question

I have a following class hierarchy, which shown in a reproduction script below:

<?php
header('Content-Type: text/plain');

class A
    {
        public $config = array(
            'param1' => 1,
            'param2' => 2
        );

        public function __construct(array $config = null){
            $this->config = (object)(empty($config) ? $this->config : array_merge($this->config, $config));
        }
    }

class B extends A
    {
        public $config = array(
            'param3' => 1
        );

        public function __construct(array $config = null){
            parent::__construct($config);

            // other actions
        }
    }

$test = new B();

var_dump($test);
?>

Output:

object(B)#1 (1) {
  ["config"]=>
  object(stdClass)#2 (1) {
    ["param3"]=>
    int(1)
  }
}

What I wanted, is that A::$config not be overriden by B::$config. There might be a lot of descendant classes from B, where I would like to change $config, but I need that those $config values to merge / overwrite if match $config values of all it's parents.

Q: How can I do that ?

I've tried to use array_merge() but in non-static mode those variables just override themselves. Is there a way to achieve merge effect for class tree without static (late static binding) ?

You probably *can* do that with a lot of `Reflection` and introspection, examining the current classes, its parent, its parent etc. and merging the arrays. See http://php.net/reflectionclass. — deceze, Jul 23 '13 at 06:31
@deceze Write answer for it, so it will be useful in future for other users. :) — Yogesh Suthar, Jul 23 '13 at 06:32

score 4 · Answer 1 · answered Jul 23 '13 at 07:27

Instead of declaring a $config property with values that you're going to change in the constructor, it's better to declare those values as default values. This is also described in Orangepill's answer:

class A
{
    public $config;

    private $defaults = array(
        'param1' => 1,
        'param2' => 2,
    );

    public function __construct(array $config = array())
    {
        $this->config = (object)($config + $this->defaults);
    }
}

A few twists there; by declaring the default value of the $config constructor argument as an empty array, you can simplify your code by using array operators like I did above. Undefined keys in $config are filled in by $this->defaults.

The extended class will look very similar:

class B extends A
{
    private $defaults = array(
        'param3' => 1
    );

    public function __construct(array $config = array())
    {
        parent::__construct($config + $this->defaults);
    }
}

@Orangepill also, it is more accurate. I end up with this, but you pointed me to reconsider `$defaults` case. — BlitZ, Jul 23 '13 at 07:57

score 3 · Accepted Answer · answered Jul 23 '13 at 06:32

3

You can restructure how your extended class is instantiated

class B extends A
{
    private $defaults = array('param3' => 1);
    public function __construct(array $config = null){
        parent::__construct($config?array_merge($this->defaults, $config):$this->defaults);
    }
}

answered Jul 23 '13 at 06:32

Orangepill

24,500
3
42
63

Tried that, will reconsider. Thanks. – BlitZ Jul 23 '13 at 06:34
Another option is you want to keep `A` intact is to make `B` an `A` [decorator](http://en.wikipedia.org/wiki/Decorator_pattern) – Orangepill Jul 23 '13 at 06:35
@CORRUPT it will work, but see the changes he has made by changing `public $config` to `private $defaults`. – Yogesh Suthar Jul 23 '13 at 06:36
@YogeshSuthar they have `protected` visibility scope in the original souce. If really, it doesn't matter `;)`. – BlitZ Jul 23 '13 at 06:47
@CORRUPT Its your choice to select best answer for your problem. :) – Yogesh Suthar Jul 23 '13 at 06:54

deceze · Answer 3 · 2013-07-23T06:48:43.677

3

You can do that using ReflectionClass. Start by introspecting $this, use getProperty(), then use getParentClass() to do the same on the parent class and its parent etc. and merge the resulting arrays together.

This is probably not the best solution for the problem you're facing though.

edited Jul 23 '13 at 06:48

answered Jul 23 '13 at 06:34

deceze

510,633
85
743
889

I like that, but there is an overheat. Hope someone might find it heandy. But not in my situation. +1 – BlitZ Jul 23 '13 at 06:49

score 1 · Answer 4 · edited May 23 '17 at 12:23

I believe the following is what you are looking for. Adapted from Inherit static properties in subclass without redeclaration?

<?php
class MyParent {
    public static $config = array('a' => 1, 'b' => 2);

    public static function getConfig() {
        $ret = array();
        $c = get_called_class();
        do {
            $ret = array_merge($c::$config, $ret);
        } while(($c = get_parent_class($c)) !== false);
        return $ret;
    }
}

class MyChild extends MyParent {
    public static $config = array('a' => 5, 'c' => 3, 'd' => 4);
    public function myMethod($config) {
        $config = array_merge(self::getConfig(), $config);
    }
}

class SubChild extends MyChild {
    public static $config = array('e' => 7);
}

var_export(MyChild::getConfig());
// result: array ( 'a' => 5, 'b' => 2, 'c' => 3, 'd' => 4, )

$mc = new MyChild();
var_export($mc->myMethod(array('b' => 6)));
// result: array ( 'a' => 5, 'b' => 6, 'c' => 3, 'd' => 4, )

var_export(SubChild::getConfig());
// result: array ( 'a' => 5, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 7, )

It works the same way for `static` classes. In my case there was non-`statics`. Still it will work, though. Thanks anyway. — BlitZ, Dec 05 '15 at 06:27

Merge array property of descendant objects

4 Answers4