I seemed to have accidently started a twitter storm debate on metaclasses in Ruby. Somethings are just are to say in 140 characters. So here’s my take on the issue.

Singleton Class / Eigenclass / Metaclass … What?

Ruby has this concept of per-class methods. In other words, you can define a method on an object, rather than on its class. Such per-object methods are callable on that object only, and not any other object in the same class.

Implementation wise, these per-object methods are defined in an almost invisible class-like object called the “Singleton Class”. The singleton class injects itself into the object’s method lookup list immediately prior to the object’s class.

Some people object to the name “singleton class”, complaining that it is easily confused with the singleton pattern from the Gang of Four book. Other suggested names are “Eigenclass” and “Metaclass”.

I objected to the use of the name “metaclass” for the singleton class on the grounds that metaclass has a well understood meaning in non-Ruby circles, and that the singleton class is not a metaclass.

So, What’s a Metaclass?

According to wikipedia:

In object-oriented programming, a metaclass is a class whose instances are classes. Just as an ordinary class defines the behavior of certain objects, a metaclass defines the behavior of certain classes and their instances.

I get two things out of this: (1) instances of metaclasses are classes, and (2) the metaclass defines the behavior of a class.

So Singleton classes aren’t Metaclasses?

No, not according to the definition of metaclass.

In general, instances of singleton classes are regular objects, not classes. Singleton classes define the behavior of regular objects, not class objects.

But Everybody Calls them Metaclasses!

I can’t change what everybody calls them. But calling a dog a horse doesn’t make it a horse. I’m just pointing out that the common usage of the term metaclass is contrary to the definition of metaclass used outside the Ruby community.

Does Ruby have Metaclasses?

Yes … I mean no … well maybe.

Is there something that creates classes in Ruby? Yes, the class Class is used to create new classes. (e.g. Class.new). All classes are instances of Class.

Is there something that defines the behavior of classes? Yes, any class can have its own behavior by defining singleton methods. The singleton methods go into the singleton class of the class.

Ruby doesn’t have a single “thing” that is a full metaclass. The role of a metaclass is split between Class (to create new classes) and singleton classes of classes (to define class specific behavior).

So, Singleton Classes Are Metaclasses?

You weren’t listening. Not all singleton classes are metaclasses. Only singleton classes of classes are metaclasses. And then only weak, partial metaclasses.

Does it Matter What We Call Them?

In the long run, probably not. Most people seem happy to (incorrectly) call them metaclasses, and this post is unlikely to change that behavior. Shoot, it seems the Rails team has already immortalized the term.

However, if reading this post has helped you understand what real metaclasses are, then it was worthwhile.

“Have I mentioned today how much git rocks?” — One of my office mates

I hear that spontaneous outpouring of appreciation for git about once a day. Usually it is someone in the office who just finished a task that would have been difficult with any of the source control systems we had used previously. Git has really impacted our day to day development process, and that’s the sign of a powerful tool.

It wasn’t always like this. I remember when EdgeCase made a rather abrupt switchover from subversion to git. I had only been dabbling with git at the time, but the guys in charge of our code repositories said “Here, this is good stuff. We’re switching … Now.”

Let me tell you, it was a little rough for a few days. Eventually we figured it out. Although we love the tool now, the learning curve was a bit steep to climb.

About two months ago we were talking in the office about git and how to encourage people to adopt it. We talked abou the need for a gentle introduction to git that quickly gets the user over the learning curve quickly. That gave me the idea for the “Souce Control Made Easy” talk that teaches the concepts behind git by starting from scratch developing the ideas behind git one by one.

A Pragmatic Screen Cast

Mike Clark of the Pragmatic Studio contacted me about turning the talk into a screencast that could reach a wider audience than the normal conference-going crowd. I’m happy to say that Source Control Made Easy is now available from the Prags.

If you are thinking about adopting git, or have already started using git but are still at the awkward stage, then this screen cast is design for you. The Pragmatic Studio page has a link to a preview of the screen cast. I hope you check it out.

Git doesn’t come with a merge tool, but will gladly use third party tools…

The Git Debate

The reoccurring debate on switching from svn to git is going on again on the Ruby Core mailing list. Amoung the many objections to git is that it doesn’t come with a nice merge tool. Perforce was held up as an example of a tool that does merging right. Although I’m not a big fan of perforce in general, the merge tool in perforce was one of its two redeeming aspects.

Now You Can Have Your Cake and Eat it Too!

Although it is correct that git doesn’t come with a nice merge tool, it is quite happy to use any merge tool that you have on hand. And since Perforce’s merge tool is available free (from here), you can use p4merge with git.

Just add the following to your .gitconfig file in your home directory:

[merge]
    summary = true
    tool = "p4merge" 
[mergetool "p4merge"]
    cmd = /PATH/TO/p4merge \
            "$PWD/$BASE" \
                "$PWD/$LOCAL" \
                "$PWD/$REMOTE" \
                "$PWD/$MERGED" 
    keepBackup = false
        trustExitCode = false

Now, whenever git complains that a conflict must be resolved, just type:

   git mergetool

When you are done resolving the merge conflicts, save the result from p4merge and then quit the utility. If git has additional files that need conflict resolution, it will restart p4merge with the next file.

Enjoy.

Interested in (not) Hearing about Git?

I’m doing a talk that’s not about git at the Ohio, Indiana, Northern Kentucky PHP Users Group (yes indeed, that acronym is OINK-PUG) on September 17th. Although the talk is explicitly not about git, you will come away from the talk with a much deeper understanding on what goes on behind the curtains with using git.

If there are other local groups interested in not hearing about git, feel free to contact me.

Update (6/Sep/09)

Several people have mentioned that it is not obvious where to get the p4merge tool from the perforce page. Go to the Perforce downloads page and click on the proper platform choice under “The Perforce Visual Client” section. When you download “P4V: The Visual Client”, you will get both the P4V GUI application and the p4merge application.

Oops, Another Update (7/Sep/09)

I forgot that the shell script that runs p4merge is something you have to create yourself. Here’s mine:

#!/bin/sh
/Applications/p4merge.app/Contents/Resources/launchp4merge $*

There are more detais Andy McIntosh’s site

Try Jay’s demo at home.

Jay Phillip’s Adhearsion Demo at the Moutain West Ruby Conf

Jay Phillip’s talk at MWRC attempted to get the audience involved in actually running an Adhearsion demo on their own laptops. Unfortunately, the demo at MWRC was plagued with firewall and network problems, but eventually I was able to get it working. Here are the steps needed.

Go ahead, try this at home. It’s a lot of fun.

Step 1—Sign up for an Adhearsion account.

You can do that here: http://adhearsion.com/signup

You will need a skype account to complete the sign-up. After signing up, you should get an email with a link that you need to click before your account is activated. Go ahead and activate the account now.

Step 2—Install the Adhearsion Gem

Run:

   gem install adhearsion

I’m running the 0.8.2 version of the gem.

Step 3—Create an Adhearsion project

Run:

  ahn create project_name

Step 4—Enable the Sandbox

Run:

  cd project_name
  ahn enable component sandbox

Step 5—Edit Your Credentials

Edit the file: components/sandbox/sandbox.yml and update the username and password you used when you created the Adhearsion account in step 1.

Step 6—Create a Dial Plan for the Sandbox

Edit the dialplan.rb file to contain the following:

adhearsion {
  simon_game
}

sandbox {
  play "hello-world" 
}

The adhearsion section should alread be in the file. You will be adding the sandbox section.

Step 7—Star the Adhearsion Server

Run:

  cd ..
  ahn start project_name

INFO ahn: Adhearsion initialized!

Errors at this stage might mean that your adhearsion account isn’t setup properly, you don’t have the right user name and password (in step 5), or that you have firewall issues preventing you from connecting to the Adhearsion server.

Step 8—Call The Sandbox

Using Skype, call the Skype user named sandbox.adhearsion.com. You should hear a hello world message.

Step 9—Change the Dial Plan

Just for fun, change the dialplan.rb file to contain:

adhearsion {
  simon_game
}

sandbox {
  play "hello-world" 
  play "tt-monkeys" 
}

(Add the tt-monkeys line to the sandbox dial plan).

Now call the sandbox again (skyping user sandbox.adhearsion.com) to hear the change in the dial plan. Monkeys FTW.

More Examples

Here’s a example of what can be done in a dial plan. I was just goofing around with my dial plan.

adhearsion {
  simon_game
}

sandbox {
  play "vm-enter-num-to-call" 
  digits = input 1, :timeout => 10.seconds
  case digits
  when '1'
    play "hello-world" 
  when '2'
    play "tt-monkeys" 
  when '3'
    play "what-are-you-wearing" 
  when '4'
    play 'conf-unmuted'
  when '5'
    play 'tt-weasels'
  when '6'
    play "pbx-invalidpark" 
  when '7'
    play "1000", "dollars" 
  when '8'
    play "followme/sorry" 
  when '9'
    simon_game
  when '0'
    play Time.now
  else
    play "demo-nomatch" 
  end
  sleep 1
  play "demo-thanks" 
}

See http://adhearsion.com/examples for more dialplan examples.

That’s It

Think about what you are doing. You are calling the Adhearsion server and controlling how that remote server responds by the adhearsion program running on your own local box. That is wild.

The adhearsion sandbox makes it easy to play around with telephony programming without any investment in the associated hardware.

I hope this demo encourages you to give Adhearsion a try.

All Rails Conf 2009 speakers are invited to a special event.

Who?

Anyone speaking at RailsConf 2009

When?

Sunday, May 3, 4:00PM – 6:00PM
(The day before RailsConf 2009 officially begins)

Where?

Las Vegas Hilton in Pavilion 1

What?

Presentations for Presenters.

Why?

You’ve come all the way to Las Vegas to tell the world about your latest Ruby/Rails project or idea. You want to make sure that you really get your message across. So, how do you do that?

The Presentations for Presenters session will give you practical tips for improving your RailsConf presentation. We will cover all aspects of planning, preparing, creating and delivering your talk, so that your unique message will get across to your audience.

Plus we will have a lot of fun. Hope to see you there.

What do I need to do?

Start planning now to attend. Since this session is actually the day before RailsConf officially begins, make sure that your travel plans gets you there in time.

If you are speaking at RubyConf this year, we have a special opportunity for you.

Are You Speaking at RubyConf 2008?

If so, congratuations! And have we got a deal for you …

Wednesday evening, Nov 5, at 6:00 pm, (that’s the night before the conference) we are inviting all speakers to a special training session. I’m going to be sharing some ideas for putting together and delivering a good presentation.

After my talk, Patrick Ewing and Adam Keys are geared up to do some Powerpoint Karaoke with everyone there. I’m not even sure what Powerpoint Karaoke is, but it sounds like fun.

I hope to see everyone there.

Update (4/Nov/08)

I’ve talked to Adam today. He says that Patrick isn’t going to able to make RubyConf this year, but we will be ready to roll with Powerpoint Karaoke anyways.

Update (5/Nov/08)

It looks like the speakers training will be in the Olympic Room tonight. The Olympic Room is on the same floor as the registration desk. Go to the left past the elevators and turn right down that hall (or ask someone who looks like they know what they are doing).

The is now a RedMine setup for Rake, FlexMock and Builder.

RedMine

As part of an effort to get better control of changes to the my open source projects, I’ve setup a RedMine issue tracking site for Rake, FlexMock and Builder. You can find it at http://onestepback.org/redmine.

Tagged

Looks like Joe O’Brien tagged me for answers to the following questions. He, in turn, was tagged by Josh Holmes, who in turn was tagged by Jeff Blankenburg. It looks like Sarah Dutkiewicz and Micheal Eaton started this.

OK, sounds like fun. Here goes.

How old were you when you started programming?

I was introduced to programming in high school by reading a book on the topic. The book taught me how to write machine code for a strange decimal-based machine. Unfortunately, there was no actual computer involved in the process. Shoot, who had computers back then? Certainly not our high school (the personal computers? not invented yet!)

In college, I learned a smattering of FORTRAN. Just enough to drive a Calcomp plotter to plot data from my undergraduate physics courses. But didn’t really get into programming until my junior year in college. (Story continued in next question)

How did you get started in programming?

So, I was planning out the courses for my junior year in college and I had a hole in my math courses. The math class I needed was not offered that semester, so my adviser suggested taking a computer programming course. He said it would be useful and, who knows, I might enjoy it.

So I signed up for an introduction to FORTRAN course, figuring it would be easy because I already knew a little bit of FORTRAN. I show up on the first day of class and after a few preliminaries the instructor jumps right into some code, that looked like this:

  (de member (pip deck) (cond
    ((null deck) nil)
    ((eq pip (car deck)) t)
    (t (member pip (cdr deck)))))

I remember scratching my head and thinking this was the strangest FORTRAN I had ever seen. I was totally confused for about three days, then something clicked on the third day of class. I suddenly “got” what the instructor was trying to get across and it all made perfect sense.

If you haven’t figured it out yet, the instructor taught us Lisp as part of an introduction to FORTRAN. The instructor turned out to be Daniel Friedman, the author of The Little Lisper, and was well known in the Lisp community. That small exposure to Lisp hooked me on programming from that point on. I took as many CompSci courses as I could in my remaining year and a half in college. I eventually graudated with a BS in Physics, but had a strong background in Computer Science as well.

What was your first language?

Technically, FORTRAN was my first language. But Lisp is the language I fell in love with and is what got me hooked on programming.

What was the first real program you wrote?

I have a very clear memory of the very first program I wrote professionally. The reason it is so clear is that this was the first program I wrote that was intended for actual use by someone who wanted it. Everything else up to that time was done for my own personal enjoyment or to satisfy some course requirement.

The program calculated the “critical angles” of “pieces”. I was given the requirements by Anne Exline, a senior programmer, and proceeded to write the program to spec. It took a few days, but when I was done I showed the result to Anne and she was pleased with the result.

The funny thing is that I had no idea what a “piece” was nor what was so critical about the angles I was calculating. I was so excited about writing an actual program that I did not ask until the software was done. When asked, Anne just looked at me funny and said “Rocket Pieces”. When Cape Canaveral lauches a rocket, they track it very carefully to make sure it stays on course. If it strays, the range safety officer is required to activate the self destruct. The critical angles are those angles that would cause the “rocket pieces” to land outside the safety area of the flight path.

So, my very first professional program was not only useful, it might actually save lives.

What languages have you used since you started programming?

Languages I have used as part of my professional career (in roughly chronological order) include FORTRAN, various assembly languages, FORTH, C, PL/M, C++, Java, Ruby.

Languages I have used in addition to those mentioned above: Pascal, Perl, Eiffel, and Lisp/Scheme.

Languages I can read, but never wrote anything significant in them: Ada, Python, Erlang, Smalltalk, SNOBOL, Algol, Pascal.

What was your first professional programming gig?

I was hired by the RCA Missile Test project in Cape Canaveral, Florida as a Near Real Time Analyst. Duties included programming various launch related software (e.g. the critical angle program mentioned above) and working launch support.

The launch support was the “Near Real Time” part of the job description. From the moment a rocket is launched until it reaches orbital velocity, any malfunction could cause it to fall back to earth. During this initial portion of the launch, the launch is monitored in “real-time” so that we know exactly where it would land if the engines were to cut off NOW. Trajectory calculations had to be done in fractions of a second and updated constantly in real time.

After the rocket reaches oribital velocity (usually somewhere between 8 and 14 minutes into its flight), it won’t fall back to earth. At this point the real time trajectory program is shut down and the near real time program is started. The near real time program can take a few minutes to calculate a more exact orbital prediction and then send that prediction to downrange radars (e.g. the the Ascension Island station) that won’t see the rocket until about 20 minutes after launch. It was the job of the Near Real Time analyst to run that program and provide oribital predictions for downrange station.

If there is one thing you learned along the way that you would tell new developers, what would it be?

Find something that you enjoy and do that. Life is too short to work in a job that you dislike.

What’s the most fun you’ve ever had … programming?

Oh, the fun I have had. This story still makes me smile.

My first computer was a single board Z80 microcomputer with 4 KB of memory. I wrote a small FORTH-like interpreter for it and hacked a version of the animal game in FORTH. The animal game is a program that plays 20 questions to figure out what animal you are thinking of. It constructs a binary tree where each node is a question and the subtrees are the yes and no answers to the question. To play the game, all the program does is walk the tree, ask the question at the current node and follow either the YES branch or the NO branch as appropriate.

If the program guesses wrong, it will ask you for your animal and a question that will distinguish your animal from the one it guessed. It then adds your question to the tree. By this extremely simple mechanism, it is able to expand its knowledge base. (see Ruby Quiz #15 for more details).

I had just finished the program and had seeded it with a single animal, a mouse. I turned to my wife and asked her to play the game. She thinks of an animal and starts the program, which immediately asked her “Is it a mouse?”. She turned to me with surprise and said “How did it know?”. Of course, the animal she picked was a mouse.

I don’t think I have ever impressed anyone with my programming skills as much as she was impressed with that game.

Who’s up next?

I’m tagging the following people. Remember, this is entirely voluntary so don’t feel obligated to answer. But I’m betting the answers are interesting:

• Chris Nelson
• Mike Clark
• Giles Bowkett
• Mark Windholtz
• Glenn Vanderburg

Conference Summary Video

Wow, what a great conference! There was a lot of energy flowing at RailsConf this year. Overall I’d rate this year as head and shoulders above last year. I’m not going cover much here, but will direct you attention to a Rails Envy VideoCase that Greg Pollack put together. The video is a series of very short interviews with a number of presenters giving summaries of their own talks. The only downside with the video is that I wish it was available before the conference. I see there were a number of interesting talks that I missed.

Followup on the “Modelling Dialogue”

Joe O’Brien, Chris Nelson and myself did a dialogue style presentation on the difference between object modelling and data modelling. The most common question I got after the talk was requests for book titles to learn more about object oriented modelling. Here are the books that Joe, Chris and I have recommended:

• Domain Driven Design—Eric Evans
• AgileSoftware Development, Principles, Patterns, and Practices—Bob Martin
• Refactoring: Improving the Design of Existing Code—Martin Fowler

The Musician’s Birds of a Feather gathering at RailsConf was great. We had a room full people, two guitars, a ukulele, a flute, several harmonicas and an improvised drum set. Unfortunately, one of the guitars was an electric travel guitar which had a dead battery, therefore no way to really hear it.

However, the other guitar was a nice Epiphone accoustic which was passed from player to player. It became the quickly became the basis for most of the music performed that night.

I want to thank Artichoke Community Music for supplying the guitar. Travelling with a guitar by plane is a big pain, so I arrived with nothing to bring to the music BOF. I called several local music stores looking for a guitar that I could rent for an evening. Artichoke music said they had a “not-for-profit” guitar that they would let me borrow for a day. Not many stores would do that for an out-of-town stranger.

So, if you’re in Portland looking for a good guitar store, check out the great people at Artichoke Community Music.