Decorator classes View as Markdown

On Thu, Dec 29, 2016 at 2:12 PM, Mathieu Rochette <mathieu@rochette.cc
mailto:mathieu@rochette.cc> wrote:

Hello internals,

I find that using the decorator pattern is very verbose and maybe
something could be done about that,
an article[1] I saw proposed a "decorates" keyword to solves this,
here is how it might look like in PHP:

interface Foo {
  public bar();
  public taz();
}

class EchoFooBar decorates Foo {
  public function bar() {
    $this->logger->debug("foo bar");
    return $this->decorated->bar();
  }
}

class LoggedFooTaz decorates Foo {
  private $logger;

  public function __construct(Foo $decorated, Logger $logger) {
    $this->logger = $logger;
    $this->decorated = $decorated;
  }

  public function taz() {
    $this->logger->debug("foo taz");
    return $this->decorated->taz();
  }
}

* the constructor is optional and default to take the first
argument and put it in $decorated
* if the constructor is provided PHP check that $decorated is set
and implements the decorated interface or class
* all public methods not overridden are automatically proxied to
the decorated object

There is at least a few different ways to go about this, the
previous example was just to give you a preview of what it could
be. If there is interest I'd like to write an RFC for this :)

What do you think about this ?


thank you


[1] https://dzone.com/articles/is-inheritance-dead
<https://dzone.com/articles/is-inheritance-dead>

-- 

Just my 2 cents:

Too much magic syntactic sugar, whereas you are just saving very
little time while implementing a few method stubs that take..
yeah it's mostly syntactic sugar, I think it would encourage developer
to use this pattern instead of inheritance when appropriate.
I also think that most of the time using the decorator pattern helps
following the single responsibility principle

also, this would add one more benefit : methods that are not override
could probably be optimized by the PHP engine (avoid one userland proxy
call)

Yet, in order to achieve that, you added a huge amount of complexity
for all the tooling that relies on the AST, including PHP itself.
.
Marco Pivetta

http://twitter.com/Ocramius

http://ocramius.github.com/

2016-12-29 16:12 GMT+03:00 Mathieu Rochette <mathieu@rochette.cc
mailto:mathieu@rochette.cc>:

I find that using the decorator pattern is very verbose and maybe
something could be done about that,
an article[1] I saw proposed a "decorates" keyword to solves this,
here is how it might look like in PHP:


* the constructor is optional and default to take the first
argument and put it in $decorated
* if the constructor is provided PHP check that $decorated is set
and implements the decorated interface or class
* all public methods not overridden are automatically proxied to
the decorated object

There is at least a few different ways to go about this, the
previous example was just to give you a preview of what it could
be. If there is interest I'd like to write an RFC for this :)

What do you think about this ?

Hi! I think that language doesn't need any additional keywords for
that. What you describe is pure class inheritance and it's already
available in the language.
It is not class inheritance, as you can see in my example, the decorator
is on an interface. one point of the decorator pattern is that you don't
need to know
which class (or subclass) you are decorating. any object implementing
the interface (or extending the class if it's a class you are
decorating) can be decorated.

To be honest I use class inheritance in Go! AOP to define decorators
because of some nice features:

1. No overhead for calling non-decorated method (we can wrap only
   required methods)

I think PHP could be smart enough to do that too for non-decorated
methods with the decorates keyword

1. Only one single instance of class, whereas traditional proxy and
   decorator pattern will use two instances (one for the original
   instance itself and one more instance for proxy/decorator)

I'm not sure decorator is appropriate here, in the article you are not
decorating[1] your class; you are outsourcing the behavior but it's not
the same

What your want can be implemented with the help of one single aspect,
applied to your codebase. Then framework will automatically create
decorators for every required class in your system. For logging
decorator example see my blogpost here:
http://go.aopphp.com/blog/2013/07/21/implementing-logging-aspect-with-doctrine-annotations/

[1] https://en.wikipedia.org/wiki/Decorator_pattern