Last night there was a very interesting extra meeting of the local AgileRTP group. Johanna Rothman was in town and Jared Richardson arranged an extra meeting so that she could present some of the issues which arise in adopting agile methods, and how to deal with them. Johanna is very knowledgeable and gave an interesting and thought provoking thought.
One of the issues she talked about was "distributed" agility. This is a hot button as many companies are outsourcing some development to "offshore" locations. Johanna talked about the issues in following agile practices, and I'm vastly oversimplifying here, pointed at time zones as the major issue.
Someone in the audience, who works in a distributed team with members across the US, questioned her on this. As the discussion unfolded, other issues came up, such as dealing with a team in China which had one person fluent enough in English who acted as the "email-translator", as well as cultural differences affecting communication.
Language and cultural differences certainly can inhibit the free exchange of information which is the coin of the realm in Agile practices, but I had to observe that these are not really geographical or time zone issues. I've seen similar difficulties with co-located teams.
Distributed development using agile methods can indeed work, I've seen it. OTI was quite good at it. We did timeboxed projects with development spread across the globe. A given project might comprise team members in Ottawa, Zurich, Sydney, Raleigh, and Vancouver. Large projects might use a "team of teams" but smaller ones had individual members who were geographically dispersed. There was lots of communication by phone and email, and it worked quite well.
OTI had one "stand-up" meeting every year, usually in February in the balmy clime of Quebec, an annual Tech Conference where everyone in the company got together at a sort of internal "OOPSLA" to talk about what they were doing and to exchange interesting ideas, and just get to know each other better.
Now the main thing that made this work was that we shared a common culture when it came to development. Although not everyone at OTI was a native English speaker, all were fluent.
"Big Dave" had a tendency to hire good people wherever he found them. Often such a person would seed a new multi-person laboratory, but sometimes a "lab" would be a single person.
So distributed development can work, and work well, given the right people.
Some agility advocates stress the need for co-location, a notable exception is Kent Beck, the founder of eXtreme Programming, who now spends most of his time based a his farm in southern Oregon, and does remote pair-programming using VNC and Skype, with programmers around the world.
And Kent is currently auctioning off a two-hour pairing session this is a good opportunity to sample distributed agility at a high level.
I wish I could afford to bid, the current bid is at $200, which is cheap. I've learned a lot every time I interacted with Kent personally in the past. Someone is going to get a deal, whatever the winning bid turns out to be.
Yesterday I took a few hours and attended an intro to SolidWorks at TechShop Durham. Then today Kent tweeted about how JUnit Max has been faring, and it got me thinking about the state of the business in software for programmers.
For those of you unfamiliar with SolidWorks, it's a 3-D Parametric Modeling program, one of the newer and most popular CAD programs. If you are a fan of the TV Show American Chopper it's the program which Jason Pohl uses to design the bikes. It has been gradually taking over the 3D mechanical CAD market, replacing old leaders like AutoCad and ProEngineer. My main interest is as a hobbyist. I've been very interested in industrial technology since I was a kid, and I like to build scale models. I'd love to have SolidWorks to play with on my own, but it's out of my price range.
SolidWorks is owned by a big corporation Dassault Systems, and it's sold through a network of VARs. Yesterdays session was given by a support engineer from the local VAR. I haven't seen an 'official' price for a license, I think they get negotiated by businesses, but I understand that the cost of a single SolidWorks 'seat' is $5,000 to $10,000 with a yearly maintenance fee of around $1000 which gets you yearly upgrades and other goodies. There's also an 'educational' license which is carefully controlled.
And that price seems well worth it to a lot of companies.
This reminds me of the way the software development tools business used to be. IBM and others got big bucks for development seat licenses for compilers, ides and other tools, sold by salesmen and supported by customer support engineers. One of the reasons Smalltalk had a hard time gaining a foothold was that ObjectWorks and VisualAge licenses were very expensive, even Digitalk Smalltalk which was targeted at the same market as Borland TurboPascal cost a few hundred bucks.
Imagine there was a time when folks actually PAID for compilers for PCs!
Nowadays that model is harder and harder to support. Most of the tools programmers use, at least the programmers I hang with, are open source, and freely available. Every once in a while a program like TextMate will pry €39 or so from a programmer's pocket, but most of us get by living off the fat of the open source land.
Unlike the proverbial shoe maker's children, it's not that we don't have any shoes, we've got all the free shoes we want.
JUnit Max, as I understand it, is an Eclipse plugin which acts as a Java equivalent to Ruby's autotest, except on steroids. While autotest runs the most recently failing test until it passes then runs all of the tests, JUnit Max queues up retests based on how recently they failed. Knowing Kent as I do, I'm sure that it's a great tool, very well crafted, but I'm just not into Java anymore, so I don't have direct experience.
Kent is asking a measly $2 per month for JUnit (at least while it's in its beta version), but judging from his tweet this morning, he's disappointed at the number of takers so far.
I admit it, we programmers tend to be a miserly lot, and a lot of us end up doing a lot of code for the love of it. We might ask for a small fee, or put up a "tip-jar" like the one on the RiCal github page but it doesn't often amount to much monetary reward.
Boy, I wish I could come up with the next SolidWorks!
One of the classics in the Smalltalk literature, which has also had a big influence on the Ruby community is Kent Beck’s “Smalltalk Best Practice Patterns”
The Ruby language has many similarities with Smalltalk, so much of Kent’s advice applies to Ruby. I frequently hear prominent Rubyists mention the book.
On the other hand, Ruby is not exactly Smalltalk, so Kent’s book isn’t an exact fit to Ruby. I’ve been wanting to start writing about adapting some of these patterns to Ruby for a while, so this article will hopefully be the first in a series.
The Motivation For This Article
Recently on the ruby-talk forum a thread discussing accessor methods vs. direct instance variable access came up. This was a hot debate topic in the Smalltalk community back in the 90s, and Kent addressed it in two competing patterns in the book, one of which Ryan Davis (a.k.a ZenSpider) brought up in the conversation.
Patterns Are Decisions, Not Prescriptions.
In their best form, patterns represent a network of decisions made during the creation of something, in this case software. A good pattern should describe the forces which affect the decision whether or not to adopt the particular solution it offers.
There can often be a tension between competing patterns, different patterns optimize different desirable characteristics, such as readability vs. flexibility.
The forces, or their relative strength, can be affected by technical factors such as the language, and features of the editor or IDE being used. To varying degrees many or all of Kent’s Smalltalk patterns have forces affected by the capabilities of the Smalltalk IDE. One of Kent’s main goals is readable code, so writing code to maximize the utility of the code exploration features of the Smalltalk browsers, inspectors, and debugger figures into the book.
A Tale of Two Patterns
Now to the specifics of the article at hand. The book has two patterns described in sequence,starting on page 89, “Direct Variable Access”, and “Indirect Variable Access”. Both address the same problem “How do you get and set an instance variable’s value?” and give two opposing solutions, along with a good discussion of the tensions.
The first pattern, as the name implies, advocates referring to an instance variable directly by name, so in Ruby, within a method, you’d just write @x, instead of using accessor methods, the second pattern.
As Kent points out in the discussion of the first pattern, direct vs. indirect access was a hotly debated topic in the Smalltalk community, although indirect access got to be popular since it was advocated by several Smalltalk training companies.
Tension Number One: Readability
In his argument for direct variable access, Kent explains that whenever he ran into an accessor method invocation, which in Smalltalk looks like this:
a = self xHe found himself pausing to remind himself that x was “just” accessing an instance variable, but that he would read the direct form:
a = xwithout breaking his stride.
I might point out that Ruby is subtly different here. First, direct instance variable access is clearly marked with the “@” sigil. On the other hand, a read accessor invocation in Ruby can be written without the explicit self receiver:
a = xSo it’s not as clear that this is a method invocation as opposed to a local variable access, although we know that it isn’t a direct instance variable access. Write accessor invocation usually requires an explicit receiver:
self.x = ato disambiguate between a write accessor call and simply assigning to a local variable, at least the first time x appears in a particular lexical scope.
Tension Number Two: Subclassablity
Although direct instance variable is more readable, it does have a drawback in that it makes certain subclassing patterns harder to implement.
If a class uses indirect variable access consistently, then a subclass can leverage this by overriding the accessor. For example, lets say we want a subclass which audits changes to an instance variable. By overriding the setter accessor it can do things like logging changes very simply. Otherwise any methods which access the instance variable in the superclass need to be overridden.
Kent’s example is defining a PolarPoint subclass of Point which has radius and theta instance variables, and overrides Point’s accessors for x and y. One interesting aspect of the Ruby/Smalltalk comparison when you look at this example a little more deeply relates to my recent article about instance variables. In Smalltalk since the Point class has x and y instance variables, it’s subclass PolarPoint would have x, y, radius and theta instance variables, although the x and y variables would be vestigial and unused. In Ruby a PolarPoint instance wouldn’t acquire the unneeded x and y instance variables.
The Encapsulation Tension
One of the reasons why there was/is such a debate between proponents of direct vs. indirect instance variable access is the effect providing setter and getter accessors has on the apparent encapsulation of the object’s state.
First, in either Ruby or Smalltalk, the mere absence of accessor methods doesn’t prevent encapsulation intrusions. Ruby has the instance_variable_get and instance_variable_set methods, and Smalltalk has instVarAt: and instVarAt:put:, but these methods are ‘marked’ as slightly evil and reserved for dastardly deeds.
An accessor method on the other hand seems much more like any other normal method. In Smalltalk, convention is used to mark methods as private, although this is very weak consisting simply of putting private methods in a particular category in the browser, with no runtime check. Ruby does provide runtime checking of both private and protected methods, although even this protection can be circumvented, using send.
Summing Up
So in the end, the existence of and the tension between these two patterns demonstrates some key points:
- Patterns present choices, and the best patterns provide enough information to make an informed decision on a case-by-case basis.
- The languages and the tools we use have an effect on the patterns and the decisions they engender.