Caius Theory

If you've not heard of it, MacRuby is an implementation of Ruby 1.9 directly on top of Mac OS X core technologies such as the Objective-C runtime and garbage collector, the LLVM compiler infrastructure and the Foundation and ICU frameworks. Basically means you write in Ruby using Objective-C frameworks, and vice versa. It's pretty damn cool to be honest!

What is +[NSObject load]?

From the documentation:

Invoked whenever a class or category is added to the Objective-C runtime; implement this method to perform class-specific behavior upon loading.

This means when your class is loaded, and implements the load method, you get a load message sent to your class. Which means you can start doing stuff as soon as your class is loaded by the runtime.

The main place I've seen it used (and used it myself) is in SIMBL plugins. A SIMBL plugin is an NSBundle that contains code which is loaded (injected) into a running application shortly after said application is launched. It lets you extend (or "fix") cocoa applications with additional features. So you have this bundle of code, that gets loaded into a running application some point after it starts, and you want to run some code as the bundle is loaded - usually to kick off doing whatever you want to do in the plugin. This is where load becomes useful.

Here's a quick implementation that just logs to the console:

@implementation MainController

+ (void) load
{
    NSlog(@"MainController#load called");
}

Now where does MacRuby come into this?

Well I came across a need to do the same in ruby, have some code triggered when the class is loaded into the runtime. Tried implementing Class.load but to no avail. Then remembered MacRuby is just ruby! And I can call any code from within my ruby class definition.

For continuity I still call it Class.load, but then call it as soon as I've defined it in the class. Eg:

class MainController

    def self.load
        NSLog "MainController#load called"
    end
    self.load

end

Of course, I'm not sure when the Objective-C method is called, it's probably after the entire class has been defined rather than as soon as load has been loaded into the runtime. So you might want to move the self.load call to just before the closing end.

Ran into a problem today where I have a class with a few attributes on it, but I only want a certain three of those attributes to appear in the YAML dump of a class instance.

Diving straight into a code example--lets say we have a Contact class, and we only want to dump the name, email and website attributes.

require "yaml"

class Contact
    attr_accessor :name, :email, :website, :telephone

    # helper method to make setting up easy
    def initialize params={}
      params.each do |key, value|
        meffod = "#{key.to_s}="
        send(meffod, value) if respond_to?(meffod)
      end
    end
end

# And create an instance for us to play with
caius = Contact.new(
  :name => "Caius",
  :email => "dev@caius.name",
  :website => "http://caius.name/",
  :telephone => "12345"
)

As we'd expect when dumping this, all instance variables get dumped out:

print caius.to_yaml
# >> --- !ruby/object:Contact 
# >> email: dev@caius.name
# >> name: Caius
# >> telephone: "12345"
# >> website: http://caius.name/

Initially I tried to override to_yaml and unset the instance variables I didn't want showing up, but that just made them show up empty. After digging around a bit more, I happened across the Type Families page in the yaml4r docs, which right at the bottom mentions to_yaml_properties.

Turns out to_yaml_properties returns an array of instance variable names (as strings) that should be dumped out as part of the object. A quick method definition later, and we're only dumping the variables we want. (See my Ruby Shortcuts post if you don't know what %w() does)

class Contact
    def to_yaml_properties
        %w(@name @email @website)
    end
end

And now we dump the class, expecting only the three attributes to be outputted:

print caius.to_yaml
# >> --- !ruby/object:Contact 
# >> name: Caius
# >> email: dev@caius.name
# >> website: http://caius.name/

Success!

There's a few useful shorthand ways to create certain objects in Ruby, a couple of obvious ones are [] to create an Array and {} to create a Hash (Or block/Proc). There's some not so obvious ones too, for creating strings, regexes and executing shell commands.

With all of the examples I've used {} as the delimiter characters, but you can use a variety of characters. Personally I tend to use {} unless the string contains them, in which case I'll use // or @@. My only exception appears to be %w, for which I tend to use ().

Strings

% and %Q are the same as using double quotes, including string interpolation. Really useful when you want to create a string that contains double quotes, but without the hassle of escaping them.

%{}                 # => ""
%Q{}                # => ""

%{caius}            # => "caius"
%{caius #{5}}       # => "caius 5"
%{some "foo" thing} # => "some \"foo\" thing"

%q is equivalent to using single quotes. Behaves exactly the same, no string interpolation.

%q{}           # => ''
%q{caius}      # => "caius"
%q{caius #{5}} # => "caius \#{5}"

Arrays

%w is the equivalent of using String#split. It takes a string and splits it on whitespace. With the added bonus of being able to escape whitespace too. %W allows string interpolation.

%w(foo bar sed)  # => ["foo", "bar", "sed"]
%w(foo\ bar sed) # => ["foo bar", "sed"]
%W(foo #{5} bar) # => ["foo", "5", "bar"]

Regexes

%r is just like using // to create a regexp object. Comes in handy when you're writing a regex containing / as you don't have to continually escape it.

%r{foo|bar} # => /foo|bar/
%r{foo/bar} # => /foo\/bar/

Symbols

%s creates a symbol, just like writing :foo manually. It takes care of escaping the symbol, but unlike :"" it doesn't allow string interpolation however.

%s{foo}      # => :foo
%s{foo/bar}  # => :"foo/bar"
:"foo-#{5}"  # => :"foo-5"
%s{foo-#{5}} # => :"foo-\#{5}"

Shelling out

%x is the same as backticks (``), executes the command in a shell and returns the output as a string. And just like backticks it supports string interpolation.

`echo hi`     # => "hi\n"
%x{echo hi}   # => "hi\n"
%x{echo #{5}} # => "5\n"

Google Groups is a pile of fail and hasn't posted my message in reply to a thread on Geekup so I'm blogging it instead.

On 27 Jan 2010, at 19:53, Steve Richardson wrote:
Thoughts?

I've been searching for a device to fit between my Macbook Pro and iPhone. I work all day on the MBP, and moving it to then watch video in another room or read twitter/news/mail whilst watching telly, etc is a pain.

The iPhone is a great little device on the move, but for trying to multitask at home it's a bit.. tedious. Even jailbroken and running multiple apps at once it's still limiting.

I'd been looking around at netbooks, but what put me off actually getting one was my previous experience with one. I know I'd want it to run OS X to keep in sync (easily) with my other Apple devices, but hackintoshing one was a bit too much hassle, plus the fact ones to hackintosh cost more than I really wanted to pay for something that wasn't quite what I thought I needed.

And then.. the iPad. I've been sort of keeping up with the rumours (mainly through Daring Fireball) and whilst I didn't get excited about it too much ahead of announcement¹, having seen the official video of it it's pretty much guaranteed that I'm going to get one.

Yes, it's limited (App Store, closed device), but.. I don't care. Take the iPhone, it's good enough for doing things on it, even if someone else is in charge of the ecosystem and has a big finger saying yes or no. I (willingly) use iTunes, Mobile Me, all the things that are so wonderfully integrated in the world of Apple, so another device that consumes my media using channels I already know and use is just a massive win for me.

All I'm hoping now is that $499 doesn't equal £499. Hopefully it'll be £399, still a good £80 above direct exchange rate, but low enough that it's a no-brainer for me to get one.

…And I think this is the first Apple product that I've seen announced and actually known from the start why I'm going to get one, instead of just a knee-jerk "SHINY!!!! WANT!!!" reaction. Uh oh, does that make me an adult?

¹ I miss getting really excited about apple announcements :(

Update

It just got even better. Was lamenting to a friend on IM that it'd be so much nicer once you can directly suck photos off a camera/SD card into it. Turns out there's an adapter for that. See "iPad Camera Connection Kit" at the bottom of http://www.apple.com/ipad/specs/ for details.

I recently came across the at(1) command, and wondered why it wasn't executing jobs I gave it on my machine. Had a poke around the man pages, and discovered in atrun(8) that by default launchd(8) has the atrun entry disabled.

To enable it (and have at jobs fire) you simply need to run the following command once:

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.atrun.plist

Personally I've taken to using this to sleep my machine after a custom amount of time, mainly because my alarm clock/sleep timer of choice (Awaken) can't handle playing Spotify for x minutes and then sleeping the machine. The following command puts the machine to sleep, which (quite effectively) silences spotify.

echo "osascript -e 'tell app \"Finder\" to sleep'" | at 1:00am

See the at(1) manpage for how to specify the time, but as I'm only ever scheduling it on the same day (usually 20 minutes or so in advance), just passing the time works fine.