PHP Any composition/inheritance solution, to avoid multiple inheritance?

Question

I'm trying to solve a design puzzle in the most efficient way, but I tend to end thinking that I really need a multiple inheritance here. So, here I am, asking the pros. I'm creating an active-record lib that will perform almost identical actions with different name and value variables. I'm on PHP 5.2.13

Suppose I have these classes:

class Property {
    protected $_props = array();

    function set($name, $value) {
        $this->_props[$name] = $value;
    };
}


class ColorProperties extends Property {
    function red($value) {
        $this->set('red', $value);
    }
    function blue($value) {
        $this->set('blue', $value);
    }
}


class LayoutProperties extends Property {
    function x($value) {
        $this->set('x', $value);
    }

    function y($value) {
        $this->set('y', $value);
    }
}

Now I need to create a class ShapeProperties that will inherit from both, ColorProperties and LayoutProperties. So that:

$shape = new ShapeProperties();
$shape->x(10);
$shape->red(255);

The reason why I need it that way, is to have auto-completion in IDE with huge PHPDoc comment block for each property. So, seems that I'm leaning towards copy/paste out of despair.

OLD BODY (BEFORE EDITS)

I've got these classes (blocks):

class Red {
    function red();
}

class LightRed {
    function light_red();
}

class Blue {
    function blue();
}

class LightBlue {
    function light_blue();
}

class Green {
    function green();
}

class LightGreen {
    function light_green();
}

And now I need to build a numerous amount of classes using these blocks, ie:

class RGB extends Red, Green, Blue {
    function red();
    function blue();
    function green();
}


class RLRB extends Red, LightRed, Blue {
    function red();
    function light_red();
    function blue();
}

So if I switch word class with interface, I'll get what I need, but I need working implementation without loads of boilerplate code. Is there a way/approach to work this around in PHP?

I'm sure your real usecase is actually a lot more complex than colors. Without really knowing what that usecase is, it's very hard to give you ideas on how to structure your code. — Evert
– Evert, Commented Jan 23, 2012 at 0:55
What is the task of a 'color' class. Can't you make a method which allows you to add 'IColor' classes. Such as Blue, Red, etc mix them (RGB) and have the result. What are you trying to achieve some kinda of highly customizable layout editor? I always try to make my code favor composition over inheritance ;) This might work for you aswell. — mark_dj
– mark_dj, Commented Jan 23, 2012 at 9:54
There's no Color class in reality, it was just to illustrate that methods are being inherited. The action is always the same in each method: function _method_name_($value) { $this->set('_method_name_', $value); }. Please refer to EDIT 2 to get more clear picture. — Aleksandr Makov
– Aleksandr Makov, Commented Jan 23, 2012 at 11:12

Louis-Philippe Huberdeau · Accepted Answer · 2012-01-22 23:50:01Z

2

You can use magic functions and delegation to do something similar. I hope your real case is not really about colors, because this would be a bit overkill to avoid a few one line functions.

You can provide an arbitrary list of implementations and cycle through them until you find one that has the appropriate method name. Call it with all of the arguments. There can be method clashes, just like it happens with multiple inheritance, except that here, no compiler will tell you. You also lose the argument validation and such.

class Color
{
    private $implementations;

    function __construct($implementations)
    {
        $this->implementations = $implementations;
    }

    function __call($functionName, $args)
    {
        foreach ($this->implementations as $impl) {
            $callback = array($impl, $functionName);
            if (is_callable($callback)) {
                return call_user_func_array($callback, $args);
            }
        }

        throw new Exception("Method not found: $functionName");
    }
}


class RGB
{
    function __construct()
    {
        parent::__construct(array(
            new Red,
            new Green,
            new Blue,
        ));
    }
}

$color = new RGB;
$color->red();

answered Jan 22, 2012 at 23:50

Louis-Philippe Huberdeau

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1 Comment

Aleksandr Makov Over a year ago

Thanks, I'll keep that solution in mind. And my real case is even worse. ALL methods share the same functionality except for the name variable that is reflecting method name. Why? Cos I need to create a library that could be used with auto-completion inside IDE, just to minimize the typo chances.

dev-null-dweller · Accepted Answer · 2012-01-22 22:55:05Z

1

In the near future it will be possible with php 5.4 new feature - traits. This will look like this:

trait RED{
  function red(){  };
}

trait BLUE{
  function blue(){  };
}

trait GREEN{
  function green(){  };
}

class RGB{
   use RED,GREEN,BLUE;
}

But for now, the best method seems to be using static methods and dependency injections, like this:

class RED{
    static function get_red($obj){
        return '0x'.dechex($obj->red);
    }
}

class RGB{
    public $red;
    public $green;
    public $blue;
    public function __construct($r,$g,$b){
        $this->red = $r;
        $this->green = $g;
        $this->blue = $b;
    }
    public function get_red(){
        return RED::get_red($this);
    }
}

$rgb = new RGB(255,255,255);
echo $rgb->get_red();

but you still have to declare all functions and make it call method from other class.

answered Jan 22, 2012 at 22:55

dev-null-dweller

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1 Comment

Aleksandr Makov Over a year ago

Thanks. Yes, traits look nice, although I'm on PHP 5.2.13. Also, yes, the main point here is to reuse as much code as possible.

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