Decorators Verses the Mix-in
It is a neat time to be involved in the Ruby community, if you ask me. A large portion of us are currently studying the techniques for doing good object oriented development. We are looking at the ideas that have come before and trying to decide the best ways to apply those ideas to our favorite language. This leads to blog posts, forum threads, and conference talks about what we are learning. No matter what, we all gain from explorations like this. Everybody wins as our collective knowledge grows. We all deserve gold stars.
So far, there's one point pretty much everyone agrees on: composition should typically be preferred to inheritance. The trickier part of that discussion though is deciding what composition looks like in Ruby. Generally you see Rubyists comparing the merits of decorators and mix-ins. [Note: the comments correctly pointed out that this was a bad use of the word "composition" on my part, to describe mix-ins.] There's a very representative thread on the excellent Objects on Rails mailing list.
I love playing with Ruby's
Hash. I think it has a neat API and experimenting with it can actually help you understand how to write good Ruby. Let's dig into this idea to see what I mean.
The nil Problem
In Destroy All Software #9 Gary chooses to show an example in Python because, unlike Ruby's
Hash, it will raise an error for a non-existent key. Ruby just returns
nil, he explains.
What Gary said isn't really true, but I'm guessing he just didn't know that at the time. He was in the process of switching to Ruby from Python and I'm guessing he just didn't have a deep enough understanding of Ruby's
Hashyet. I bet he does know how it works now.
But assume he was right. What's he saying and why does it matter? Consider some code like this:
class SearchesController < ApplicationController def show terms = params[:terms] SomeModel.search(terms) # ... end end
This is what Gary doesn't like, and rightfully so. Because I indexed into
paramshere with the
()method, I will indeed get a
:termskey wasn't in
Single Method Classes
[Update: I've changed my mind about some of the following due to this excellent counter argument.]
In the words of Dennis Miller, "I don't want to get off on a rant here, but…"
There's something that drives me crazy and I see it in so much Ruby code. I see it in the documentation for our key projects; I see Rubyists of all skill levels doing it; it's just everywhere.
Let's talk about when the use of a
Classis and is not appropriate.
The Chained new()
Here's an example of one form of code that bugs me:
class Adder def add(n) 40 + n end end p Adder.new.add(2)
The problem here is that a
Classhas been used, probably because as Rubyists that's always our default choice, but it's the wrong fit for this code. A
Classis for state and behavior. The example above is just using behavior. No state is maintained.
A handy tip for sniffing out this problem is watching for a call to
new()in the middle of method chaining as we have here. If you always use a
Classlike that, it's not really a
Class. Put another way, if an instance never gets assigned to a variable, something has likely gone wrong with the design.
Let's Patch Rails
In celebration of my first ever trip to RailsConf next week I wanted to be a good open source citizen and contribute a patch.
I'm giving a presentation at the conference on various random features that the framework provides. I selected features from many places like blog posts, books, and some that I just remembered from years of working with the software.
One of the features I decided to show was an old feature that I never see anyone use. It turns out that there's a good reason for that. When I tried it on a modern Rails, it didn't work anymore. Rails has undergone some changes under the hood and this feature was likely removed in that process. I figured out a workaround so I could still show it in my presentation, but it would be nice if I contributed the fix back to Rails so others could use it.
In this article, I will walk through the entire process of doing that.
ERb has always had an under appreciated syntax tweak. Everyone knows you can write code like this:
Riding the Testrocket
I say it a lot, but programming is about ideas. More specifically, it's about not running out of ideas.
Along these lines, I read the results of an interesting study recently. It was a study about how we think and solve problems. When I was in school, the belief was that we needed to cram our brain full of facts. We were pushed to memorize, memorize, memorize.
The more modern view of learning is that facts don't matter as much. Nowadays we just try to teach children how to think. The assumption is that they can find the facts they need, because information is so universally available, and their thinking skills will allow them to work their way to other bits of knowledge.
The study looked at people taught using both of these techniques and found some surprising results: us memorizers can often out think the thinkers. A leading theory about why that's the case is that the memorizers have more of a foundation to build their ideas off of. Thinkers may be starting closer to scratch each time. If so, they have further to go to get to the needed solution. Memorizers, on the other hand, may already have a lot of knowledge that puts them closer to the solution before they even need to start thinking.
A Stylish Critique
Before getting started, I feel compelled to point out that my dictionary defines a critique as "a detailed analysis and assessment of something." It seems like we often assume the worst of that word, but that's not how I intend it here.
The Ruby community seems to be talking about style guides lately. So let's talk about them.
The fact is that you will have many choices if you go looking for style guides for our favorite language. You can pick from:
- The old stuff
- Google's way
- GitHub's popular guide
- Guides from respected Rubyists, like Dan Kubb
- One of the many forks of the popular guides on GitHub
- And many more
It's obvious that Rubyists care about this topic. Let's see what's out there and consider what really is and is not useful from these guides.
What is a style guide really, and why do we even have them?
Defining style guides is surprisingly tough. I suspect they started out as formatting rules for code, but they have evolved pretty far beyond that now.
Most guides include general conventions that the author feels are important when writing the language in question. This can go all the way down to how to use certain constructs, opinions on what the author considers idiomatic, and syntax to outright avoid.
Learn to Love Mix-ins
The road to mastering Ruby is paved with understanding some key Ruby concepts. Mix-ins are one of those concepts. I'm sure everyone reading this knows the mechanics of how mix-ins work, but it pays to spend some time really thinking about all that mix-ins imply. Let's do just that.
Adding a Type
One of the primary reasons that Ruby needs mix-ins is that it does not support multiple inheritance. That leaves mix-ins as our only option for modeling hybrid objects. It's the way Ruby programmers can add another type.
That's a good way to think about it too: adding a type.
Take pagination, for example. Pagination methods are usually defined to return an object like this:
class PaginatedCollection < Array # ... paginated helpers defined here ... end
That's never really felt right to me though.
First, inheriting from Ruby's core classes can come back to bite you in some scenarios. The reason is that Ruby makes some performance tradeoffs to keep the core classes fast, but those tradeoffs mean that those classes don't always perfectly follow Ruby's rules.
When Passion Goes Wrong
I usually stick to pretty code heavy topics in these articles, but please allow me to take a detour this time. Our industry struggles with a problem that we don't discuss enough and I want to give it some air time.
The fact is, we're pretty lousy at controlling stress.
Let's look at why that is and some of the ways this problem manifests. Remember, the first step is admitting that we have a problem.
We are a Passionate People
I really believe good programmers are passionate about what we do. Our job can be pretty mentally taxing and, if you don't love it, it would be pretty rough to endure that day in and day out.
Because of that, we generally find that the programmers who survive the climb are passionate folks. Really think about that for a minute. I'll give some examples.
Kent Beck is a name I bet most of us know. One of his great successes was actually writing a book of guidelines for how individual lines of code should be structured. He had to care about the individual lines. That's how far he had to go to manage his programming. He's also done a ton for testing, for similar reasons.
The Right Ruby Mix
Ruby is a melting pot language. It borrows ideas from many things that came before. It combines several different programming philosophies.
This aspect of the language can be a plus. It means that Ruby is suited to multiple applications. It also opens up some pragmatic shortcuts. Even better, it sometimes encourages us to think about problems using a different lens of thought.
Of course, this cuts both ways. Ruby living at the intersection of many ideas does have some downsides. First, there's more to learn than you find with some simpler languages. There's a cost for the extra knowledge we have to track. Even worse though, in my opinion, is that it's sometimes hard to know exactly what Ruby's style really is.
Going Off Script
One culture Ruby borrowed heavily from is that of the so called "Scripting Languages." The main source of these features was Perl, in my opinion, but you can also find influences from Bash and other sources. I found this comforting since I came to Ruby from Perl, but the truth is that it bothers some people.
Refactoring: The Gilded Rose
It's time for another refactoring challenge. This time we will attempt a fun problem called The Gilded Rose Code Kata.
That original description of the problem was for C# developers and it didn't have things us Rubyists love, like tests. Luckily for us though, Jim Weirich ported the code to Ruby and added the tests as he did so. Let's use that version of the challenge.
As always, I recommend you try the refactoring before you read what I have to say about it. Being familiar with the problem will help you understand what we are dealing with below.
The first step in this problem is to get the code running locally. I started by pulling down Jim's code from GitHub:
$ git clone https://github.com/jimweirich/gilded_rose_kata.git Cloning into gilded_rose_kata... remote: Counting objects: 114, done. remote: Compressing objects: 100% (46/46), done. remote: Total 114 (delta 71), reused 109 (delta 66) Receiving objects: 100% (114/114), 15.38 KiB | 13 KiB/s, done. Resolving deltas: 100% (71/71), done. $ cd gilded_rose_kata