Quick Ruby Quiz

I was talking to the Dallas Ruby group a couple of days ago, and showed them the following code:

class Fred
  class << self
    def self.say_hello
      puts "Hi!"
    end
  end
end

Someone asked whether it was possible to call the say_hello method. It is. How many ways can you find?

Comments

[Mariano Kamp]

I can just think of two so far ...

one:

class << Fred
self.say_hello
end

two:
class Object
def singleton_class
class << self; self; end
end
end
Fred.singleton_class.say_hello

ps. Nice idea with the Erlang book!

[Tim]

(class << Fred ; self ; end).say_hello

[Mariano Kamp]

Oh, and I missed at least one pretty obvious ones.

Fred.new.class.singleton_class.say_hello

[Drew Raines]

Fred.class_eval{class << self; self end}.say_hello

[Mark Howe]

Here is another variation:

class Fred
class << self
self.say_hello
end
end

[Dave Dunkin]

Wow, the readability of that almost reminds me of Perl. Just because something can be done does not mean it should.

[Herryanto Siatono]

My mistake for the prev entry. Sorry!

[Herryanto Siatono]

My other attempt:

class Fred
class << self
def inner_class
class << self; self; end
end
end
end

Fred.inner_class.say_hello

[Curt Sampson]

You know, this is one of the terrible things about Ruby. Building applications is hard; it doesn't help to have puzzles in your language, as well.

[Dave Thomas]

Curt: I disagree. Any decent, interesting language is going to allow you to express your applications cleanly and elegantly. But, at the same time, it will have a depth to it which gives it power. This is an example of that depth. It isn't a puzzle as much as a way of learning about metaclasses. Understand this, and you'll understand a whole bunch of the Ruby MOP.

Dave