If you are considering releasing your Ruby project as a gem, you might want to see this (or this if you are using Rake).

Anyone want to make a guess when we will hit 100 gems?

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The biggest change is that FileList are now "load on demand". When you define a file list, e.g.

   PKGFILES = FileList['**/*.rb', 'test/*']
   PKGFILES.exclude(/^temp/)

The file list just records the include and exclude patterns. Later, when you do …

  PKGFILES.each { |filename| ... }

the file list will actually go out and read the file system to find the matching files. The thought is that searching the file system is a rather expensive operation and if you never actually use the file list, then it is wasted time. By building the file list only when it is needed will make rake startup time a bit faster.

If you are having trouble starting with rake, I wrote up a QuickStartExample showing off some of the features of rake.

What is Rake?

Rake is a make-like utility written entirely in Ruby. It allows to you specify build target and actions, with the action being standard Ruby code.

Download

You can get Rake from rubyforge. If you have rubygems installed, then all you need to do is …

  gem -i rake

If you have a very recent version of rubygems (i.e. from CVS), then the —gen-rdoc option finally produces a decent rendition of the Rake documentation locally.

Way back when, I used to work on a data acquisition system that used an IRIG clock reader to timestamp our data samples. An IRIG clock works by reading a signal that sends the time once every second. Between the second ticks, the clock reader would interpolate the time down to the millisecnod level. This allows you to have several clocks on different systems all synchronized to the same clock signal.

Our system had to take a sample every 20 milliseconds, so every cycle we would calculate the time of the next cycle. When the current data cycle was done, we would just wait until that next scheduled time arrived to start the next cycle.

An IRIG clock reader is an interesting device. Normally it works really well, but occasionally (especially if there is noise on the clock signal line) it will misread the time signal. One particular reader we were using tended to misread a couple of bits in the minutes data with the result that for one second, the clock reader would add 30 minutes to the real time. When the next clock signal arrived a second later, the reader would start reporting the correct time again.

Jumping ahead was no problem. Our software just used the reported time and continued to schedule data cycles. However, when the clock jumped backwards, the next data cycle was suddenly scheduled for 30 minutes in the future. The result was that our system mysteriously stopped dead for 30 minutes and then just as mysteriously restarted as if nothing happened.

Time is a strange concept in computer programs. It is difficult to know what the exact time is while executing. Consider the following lines of code …

   t = Time.now                      # Line 1
   puts "The Current Time is: #{t}"  # Line 2

One would think that line 2 will print the current time. And most of the time we would be correct. But suppose I pressed the suspend button on my laptop between line 1 and line 2. It might be hours (or days) before line 2 prints out its now "out-of-date" time message.

When you are dealing with times in the millisecond range, there are all kinds of things that will pause your program from one line to the next. Interrupts, page faults, and time slicing all interact in interesting ways to make the concept of "time" in a program something of a challenge.

It wasn’t hard to fix our cycle scheduler to be well behaved, even in the face of uncertain time. And I learned a new respect for time in the process.

I’ll reproduce his summary here:

• Everything is an object

    5.times do print "hello world".capitalize end
  

• Elegant blocks gives inline power

    db.select_all(sql).inject([]) do |objects, row|
      objects << instantiate(row)
    end
  

• Exploring with reflection
• Extending at runtime (even standard lib!)
• Extensive standard library
  • XML, Test/Unit, Distributed Ruby, XML-RPC, WEBrick

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Sometimes, however, you don’t want to start with all those methods. I’m thinking of proxy classes that use method_missing to forward messages to another object. Methods defined by Object (actually Kernel, but lets not worry about that) will not be forwarded because they are not missing in the proxy.

This is easy to fix. Create a BlankSlate class like this …

  class BlankSlate
    instance_methods.each { |m| undef_method m unless m =~ /^__/ }
  end

BlankSlate is a class with no instance methods except for __send__ and __id__.

Now we can create a proxy object by inheriting from BlankSlate …

  class Proxy < BlankSlate
    def initialize(obj)
      @obj = obj
    end
    def method_missing(sym, *args, &block)
      puts "Sending #{sym}(#{args.join(',')}) to obj"
      @obj.__send__(sym, *args, &block)
    end
  end

Now, try this with the proxy object:

  n = Proxy.new(1)
  puts (n+5)
  puts "1.id = #{1.id}"
  puts "n.id = #{n.id}"
  puts "n.__id__ = #{n.__id__}"

Here’s the output:

  $ ruby blankslatedemo.rb
  Sending +(5) to obj
  6
  1.id = 3
  Sending id() to obj
  n.id = 3
  n.__id__ = 537806934

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1. To create an environment where the object under test can live.
2. To test that the object under test correctly modifies the environment.

Each use requires a slightly different API (#1 sytle APIs tend to be more flexible than style #2). I’ve used both styles of APIs in the past (and had been frustrated trying to use a style #2 API in a style #1 situation), but I hadn’t connected the differences with the reason for the differences before.

Here’s what I did. First download the tar or zip file (as you need) from here. Then …

  $ tar zxvf instiki-0.3.1.tgz
  (lot of output omitted)
  $ ruby instiki.rb 2500

Now you have a wiki server running locally on your computer. To see it, direct your browser to localhost:2500 and edit away.

What is a Wiki you ask? A Wiki is a set of web pages that can be easily edited from a browser. Hyperlinks within a Wiki are easy to setup and generally are keyed off of words with special capitalization. New pages can be created at the drop of a hat and the pages are always live and changable. Formatting rule are usually very simple, for example asterisks surrounding a word can make it *bold*.

Wikis are great for collaborative web sites, where everyone contributes a bit here and a bit to build the site. I’ve used Wikis to coordinate software projects and provide documentation.

Instiki uses RedCloth, a Ruby implementation of Textile to handle the formatting. Although a bit different from the formatting rules used by traditional Wikis, Textile looks to be very flexible in the kind of HTML it is able to produce. Yet it doesn’t seem to get in the way of just entering text.

Update: Instiki now as its own domain: www.instiki.org. I’ve updated the home page link in article.

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I was using Internet Explorer at work (that’s not the weird part), and today I used it to browse to my blog. Imagine my surprise when I discovered that the new CSS look for my site was gone! The site was being rendered in the old-style CSS! I switched back to FireFox (mozilla) and sure enough, the new look was still showing up there. It is only under Internet Explorer that the new CSS fails to show up.

I’m not even sure how it is possible to IE to screw up? I mean, the old CSS files weren’t even on my server anymore (unless I screwed up somewhere). The new CSS file has a different name and is in a different location, so a cache problem seems unlikely. This is just bizarre.

Since I don’t run IE at home (I’m Linux only at home), I don’t know if this is a work related proxy/caching anomoly, or if IE everywhere has this problem.

So … If you are using Internet Explorer to view this site, let me know if it looks like the new style or the old style. (Click on the links to see screen shots).

Thanks. You can drop me an email at jim@weirichhouse.org or use the Wiki feedback link below.

UPDATE!

For some reason, I got it in my head that a "#" character was a comment in CSS. Evidently it is not, it is just bad syntax. Mozilla based browsers tend to drop the line that contains the hash mark. IE just skips the hash mark and continues. As I was reworking the CSS file, I commented out the old colors and added the new stuff. IE overrode the new colors with the old "not quite commented out" colors. Mystery explained.

FYI, apparently CSS uses C style /* … */ comments. Well, now I know.

Thanks to Gabriele Renzi who pointed out the problem and to Andrew Johnson who supplied the link www.danvine.com/iecapture that I used for testing IE from home.

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The Once and Future Perl

I had switched to using Ruby (from Perl) about 6 months earlier at that time, and I had a chance to talk to Larry about the changes in OO support that he wanted in Perl. I remember him commenting that Perl5 made OO possible, but not necessarily convenient.

In his Apocalypse series, Larry describes the direction Perl 6 will be taking in several areas. Three years after that talk, Apocalypse 12 is available, and it addresses the details of Object Orientation in Perl 6.

I just want to point out that all the examples in this blog entry are directly from the apocalypse.

Objects in Perl 6

I skimmed the article last night and jotted down some notes. You will need to read the apocalypse yourself for any substantial details (its a long article, 20 pages in all). I’m just going touch on some highlights and first impressions.

Objects in Perl 5 were built out of the existing language framework. Blessing was the only new piece added to Perl to support objects, hash, packages and namespaces were all existing Perl concepts. And although it worked, it left the Object Model of Perl very open to variations.

Perl 6 adds more language support for direct support of objects, and leave less to programmer choice. Here is a point object in Perl 6:

    class Point {
        has $.x;
        has $.y is rw;
        method clear () { $.x = 0; $.y = 0; }
    }

Notice the keywords for class and the declaration of attributes $.x and $.y. The $.x attribute is publicly readable, and the $.y is publically writable as well. Private attributes can be declared with a colon instead of a period (e.g. $:z).

Methods are part of the class declaration now and are syntactically differentiated from normal subroutines by using the "method" keyword.

ISA vs HASA

In OO circles it is said that HASA relationships should be modeled by composition and ISA relations by inheritance. Although I find that saying to be a bit simplistic, it is cool that Larry makes that connection explicit by his choice of keywords. Did you notice in the above example that the attributes were introduced by the keyword has?

So its not surprising that inheritance is introduced with the is keyword. Here’s another simple example building on the previous one:

    class Point3d is Point {
        has $:z = 123;
        method clear () { $:z = 0; next; }
    }

The is keyword is overloaded (this is Perl after all). Traits are also declared using the is keyword. That leads to interesting code like:

    class Moose is Mammal is stuffed is really(Hatrack) is spy(Russian) {...}

Roles

Although Perl 6 will support inheritance (single or multiple), it also contains the idea of Roles. My impression of a Role is that is a cross between Ruby modules and Java interfaces.

Roles look a lot like classes, but they cannot be instantiated. Roles cannot inherit from classes, but they can be composed with other roles.

Here is an example role. Notice that the method feed depends upon the method call should should be defined in the final objects.

    role Pet {
        method feed ($food) {
            $food.open_can();
            $food.put_in_bowl();
            .call();
        }
    }

Roles are attached to classes with the does keyword:

    class Dog {
        is Mammal;
        does Pet;
        does Servant;
        does Best::Friend[Man];
        does Drool;
        ...
    }

So far Roles look very much like Ruby modules. However, here is a twist. If the methods in roles are only declared instead of defined, then the Role specifies the methods expected to be implemented in the class. One final example.

    role Pet {
        method feed ($food) {...}
        method groom () {...}
        method scratch (+$where) {...}
    }

The {…} construction means that the body of the method is defined elsewhere.

Stuff I Left Out

This Apocalypse runs 20 pages. Its obvious that I skipped over a lot of material. It seems like the OO support in Perl 6 is much better than Perl 5. The object module is very flexible (a good thing), but also rather complex (a not so good thing). Larry addresses some really interesting problems (such as multiple dispatch), and it will be interesting to watch to see if the features really work together or not.

Am I switching? No, not really. I really much prefer the much simplier object model (and syntax!) provide by Ruby. But I will be watching.

Some Great Quotes

Larry is great for generating good quotes. I’ll end this entry with a few quotes that struck me.

It has often been claimed that Perl 5 OO was "bolted on", but that’s inaccurate. It was "bolted through", at right angles to all other reference types, such that any reference could be blessed into being an object. That’s way cool, but it’s often a little too cool.

Here’s another one:

Some people will be surprised to hear it, but Perl is a minimalist language at heart. It’s just minimalistic about weird things compared to your average language.

And speaking of chosing a keyword to distinguish typing from subtyping:

On the other hand, a bit confusingly, it looks like subtyping will be done with the "type" keyword, since we aren’t using that word yet.

Closing Joke

For some reason, I found this extremely funny:

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