奇怪的PHP装饰模式输出

Question

I have implemented a basic snipe of code based in decorator pattern.

Decorator class:

abstract class HTMLDecorator {

    /** @var \ArrayObject */
    protected $notes;

    public function format(){
        $html = '';

        foreach ($this->getNodes() as $node)
            $html .= "<p>{$node}</p>";

        return $html;
    }
}

This is the base class:

class HTML extends HTMLDecorator{

    public function __construct(){
        $this->nodes = new \ArrayObject();
    }

    public function getNodes(){
        return $this->nodes;
    }
}

Now, these two classes add nodes to the html array.

Block:

class BlockHtml extends HTMLDecorator{

    protected $html;

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

    public function getNodes()
    {
        $this->html->getNodes()->append('Block html');
        return $this->html->getNodes();
    }

}

Image:

class ImageHtml extends HTMLDecorator{

    protected $html;

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

    public function getNodes()
    {
        $this->html->getNodes()->append('Image html');
        return $this->html->getNodes();
    }

}

Finally, I have tested it as doing:

$html = new HTML()
$html = BlockHTML($html);
$html = ImageHTML($html);
echo $html->format();

The result is:

Block html
Image html
Block html

Why does code print "Block html" twice?

Answer 1

Calling $html = ImageHTML($html); using the result obtained from $html = BlockHTML($html); might causing the problem. Can you try to assign the returned value to different variable and assemble it at the end.