RendererDecorator class should implement RenderableInterface

[adayth]

RendererDecorator.php has this comment but it dosen't implements the interface.

/**
 * the Decorator MUST implement the RendererInterface contract, this is the key-feature
 * of this design pattern. If not, this is no longer a Decorator but just a dumb
 * wrapper.
 */
abstract class RendererDecorator {}

[ihor]

Funny thing that in my GoF book there is a mention that another name for Decorator is Wrapper :)

Anyway, I think forcing the interface is a useful thing but PHP allows us to simplify Decorator implementation in a case which is not present in this repo. Current implementation shows only one limited use case of Decorator pattern and is not showing the all fun stuff you can do.

This is a picture from my GoF book and as you can see this repo shows us only the BorderDecorator example (which is not actually true because BorderDecorator adds a new state and the implementation in this repo only decorates the existing behavior).

But with Decorator not only you can decorate the existing behavior but also add a new one. Like in ScrollDecorator adds ScrollTo method which is not present in the decorated object.

And as you can see in this case it is much easier to proxy method calls to the decorated object using magic __call method than using an interface.

So my suggestion is to change the whole Decorator example. I would make a PR but I don't have much time now. But maybe later if @domnikl agrees with what I said above.

[adayth]

Sounds interesting to me @ihor maybe you can do something fast in a gist, as example.
Homever, PHP magic methods generally are considered a bad practice, so I think that the implementation could be more clean without them.

[ihor]

It is a trade-off: benefits of using an interface on one side and simpler implementation on another.

Nobody complains about using magic methods in Proxy pattern implementation in PHP. As well as nobody complains about using magic methods in Python. It is a powerful concept which allows us to write simpler code when used appropriately.

I'll think about some nice example which would make sense in PHP. I tried to Google for good examples quickly but it is really hard since most of the examples are the same as in this repo (caused by the language limitations). A couple of links where you can see what I'm talking about:

• http://advancedcppwithexamples.blogspot.com/2010/09/c-example-for-decorator-design-pattern.html
• https://github.com/ezimuel/PHP-design-patterns/blob/master/Decorator.php

[adayth]

The second example (the github link) seems good to me.

[domnikl]

@ihor I agree, but could we not just extend the example and let RendererDecorator implement RenderableInterface and add some additional behavior to JsonRenderer like a method formatOutput()? Anyway, whenever you got some time, send me a PR and I will have a look.

[ihor]

@domnikl sure, it should implement an interface in this example.

[andrewnester]

Hi @domnikl @ihor @adayth !
I've just added PR to fix this issue.

[piotrgradzinski]

Since the PR is merged and I can't see any other things to discuss I am closing this issue.