Open Stack

Regarding use of the final keyword and limiting extending in general, a few thoughts below:

- While I found the blog post about final classes to be informative, I'd take it with a grain of salt. The author bills himself as a consultant who works with enterprise web applications. Briefly looking at his background, practically all his gigs were short consulting jobs. I don't see a track record for open source projects so it would appear that his views are likely more applicable for enterprise developers working within closed systems.
- The Java community has already beaten this subject to death over the past decade. During recent years, it seems that the debate has waned. I occasionally see enterprise Java devs use final to communicate their intent so that their system isn't butchered many years down the road when it becomes poorly understood legacy code. 
- On the other hand, I hardly ever see final classes in open source code/APIs. 
- Regarding future-proofing, I agree that it's easier to switch from final to not using final than the other way around. However, I've actually had cases where I needed to extend a final class in an API and was simply annoyed by the author's desire to control how I use the API. I also understood that if the author were to change certain things, my extension may have to be refactored. That's a risk I'm certainly willing to take to get the job done.

Thanks,
--
Sam Choi
Hewlett-Packard Co. 
HP Cloud Services
+1 650 316 1652 / Office


-----Original Message-----
From: Matthew Farina [mailto:matt at mattfarina.com] 
Sent: Monday, June 09, 2014 7:09 AM
To: Jamie Hannaford
Cc: Shaunak Kashyap; Glen Campbell; OpenStack Development Mailing List (not for usage questions); Choi, Sam; Farina, Matt
Subject: Re: [openstack-sdk-php] Use of final and private keywords to limit extending

If you don't mind I'd like to step back for a moment and talk about the end users of this codebase and the types code it will be used in.

We're looking to make application developers successful in PHP. The top 10% of PHP application developers aren't an issue. If they have an SDK or not they will build amazing things. It's the long tail of app devs. Many of these developers don't know things we might take for granted, like dependency injection. A lot of them may writing spaghetti procedural code. I use these examples because I've run into them in the past couple months. We need to make these folks successful in a cost effective and low barrier to entry manner.

When I've gotten into the world of closed source PHP (or any other language for that matter) and work that's not in the popular space I've seen many things that aren't clean or pretty. But, they work.

That means this SDK needs to be useful in the modern frameworks (which vary widely on opinions) and in environments we may not like.

The other thing I'd like to talk about is the protected keyword. I use this a lot. Using protected means an outside caller can't access the method. Only other methods on the class or classes that extend it.
This is an easy way to have an API and internals.

Private is different. Private means it's part of the class but not there for extended classes. It's not just about controlling the public API for callers but not letting classes that extend this one have access to the functionality.

Given the scope of who our users are...

- Any place we use the `final` scoping we need to explain how to extend it properly. It's a teaching moment for someone who might not come to a direction on what to do very quickly. Think about the long tail of developers and projects, most of which are not open source.

Note, I said I'm not opposed to using final. It's an intentional decision. For the kinds of things we're doing I can't see all to many use cases for using final. We need to enable users to be successful without controlling how they write applications because this is an add-on to help them not a driver for their architecture.

- For scoping private and public APIs, `protected` is a better keyword unless we are intending on blocking extension. If we block extension we should explain how to handled overriding things that are likely to happen in real world applications that are not ideally written or architected.

At the end of the day, applications that successfully do what they need to do while using OpenStack on the backend is what will make OpenStack more successful. We need to help make it easy for the developers, no matter how they choose to code, to be successful. I find it useful to focus on end users and their practical cases over the theory of how to design something.

Thoughts,
Matt


On Fri, Jun 6, 2014 at 10:01 AM, Jamie Hannaford <jamie.hannaford at rackspace.com> wrote:
> So this is an issue that’s been heavily discussed recently in the PHP 
> community.
>
> Based on personal opinion, I heavily favor and use private properties 
> in software I write. I haven’t, however, used the “final” keyword that much.
> But the more I read about and see it being used, the more inclined I 
> am to use it in projects. Here’s a great overview of why it’s useful 
> for public
> APIs: http://verraes.net/2014/05/final-classes-in-php/
>
> Here’s a tl;dr executive summary:
>
> - Open/Closed principle. It’s important to understand that “Open for 
> extension”, does not mean “Open for inheritance”. Composition, 
> strategies, callbacks, plugins, event listeners, … are all valid ways 
> to extend without inheritance. And usually, they are much preferred to 
> inheritance – hence the conventional recommendation in OOP to “favour composition over inheritance”.
> Inheritance creates more coupling, that can be hard to get rid of, and 
> that can make understanding the code quite tough.
>
> - Providing an API is a responsibility: by allowing end-users to 
> access features of our SDK, we need to give certain guarantees of 
> stability or low change frequency. The behavior of classes should be 
> deterministic - i.e. we should be able to trust that a class does a 
> certain thing. There’s no trust whatsoever if that behavior can be edited and overridden from external code.
>
> - Future-proofing: the fewer behaviours and extension points we 
> expose, the more freedom we have to change system internals. This is 
> the idea behind encapsulation.
>
> You said that we should only use private and final keywords if there’s 
> an overwhelming reason to do so. I completely disagree. I actually 
> want to flip the proposition here: I think we should only use public 
> keywords if we’re CERTAIN we want to encourage and allow the 
> inheritance of that class. By making a class inheritable, you are 
> saying to the outside world: this class is meant to be extended. And the majority of times this is not what we want.
> Sure there are times when inheritance may well be the best option - 
> but you can support extension points in different, often better, ways. 
> Declaring explicitly what the extension points are is part of the 
> contract your code has with the rest of the system. Final classes help 
> to enforce this contract.
>
> To summarize, we have nothing to lose by favoring private and final 
> keywords. We gain the above advantages, and if we later decide to open 
> up that class as an extension point we can remove the keywords without 
> any issues. Should a valid reason come up to open it up, it will be 
> easy to do so, because nothing depends on it being closed. On the 
> other hand, if you start by making everything open or inheritable, it 
> will be very hard to close it later.
>
> Jamie
>
> On June 5, 2014 at 6:24:52 PM, Matthew Farina (matt at mattfarina.com) wrote:
>
> Some recent reviews have started to include the use of the private 
> keyword for methods and talk of using final on classes. I don't think 
> we have consistent agreement on how we should do this.
>
> My take is that we should not use private or final unless we can 
> articulate the design decision to intentionally do so.
>
> To limit public the public API for a class we can use protected.
> Moving from protected to private or the use of final should have a 
> good reason.
>
> In open source software code is extended in ways we often don't think 
> of up front. Using private and final limits how those things can 
> happen. When we use them we are intentionally limiting extending so we 
> should be able to articulate why we want to put that limitation in 
> place.
>
> Given the reviews that have been put forth I think there is a 
> different stance. If there is one please share it.
>
> - Matt
>
>
>
> Jamie Hannaford
> Software Developer III - CH
> Tel: +41434303908
> Mob: +41791009767
>
>
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