how to implement a decorator in PHP?

Question

Suppose there is a class called "Class_A", it has a member function called "func".

I want the "func" to do some extra work by wrapping Class_A in a decorator class.

$worker = new Decorator(new Original());

Can someone give an example? I've never used OO with PHP.

=======================================================

Thank you guys,you've provided a good demo for me!

Is the following version right?

class Decorator
{
    protected $jobs2do;

    public function __construct($string) {
        $this->jobs2do[] = $this->do;
    }

    public function do() {
        // ...
    }
}

The above code intends to put some extra work to a array.

Answer 1

That is pretty easy, especially in a dynamically typed language like PHP:

class Text {

    protected $string;

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

    public function __toString() {
        return $this->string;
    }

}

class LeetText {

    protected $text;

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

    public function __toString() {
        return strtr($this->text->__toString(), 'eilto', '31170');
    }

}

$text = new LeetText(new Text('Hello world'));
echo $text; // H3110 w0r1d

You may want to have a look at the wikipedia article, too.

Answer 2

I would suggest that you also create a unified interface (or even an abstract base class) for the decorators and the objects you want decorated.

To continue the above example provided you could have something like:

interface IDecoratedText
{
    public function __toString();
}

Then of course modify both Text and LeetText to implement the interface.

class Text implements IDecoratedText
{
...//same implementation as above
}

class LeetText implements IDecoratedText
{    
    protected $text;

    public function __construct(IDecoratedText $text) {
        $this->text = $text;
    }

    public function __toString() {
        return str_replace(array('e', 'i', 'l', 't', 'o'), array(3, 1, 1, 7, 0), $this->text->toString());
    }

}

Why use an interface?

Because then you can add as many decorators as you like and be assured that each decorator (or object to be decorated) will have all the required functionality.

Answer 3

I second the use of an interface. It's especially informative with the decorator pattern. After all, it's not just the compiler/interpreter you're instructing, sometimes it's actually helpful to instruct other people as well, who're just trying to figure out what the h*ll it is that you're trying to accomplish ;)