From: Patrick Hurley <phurley@...>
Date: 2005-12-21T13:36:26+09:00
Subject: Re: When are attr_reader type methods called?

On 12/20/05, Vivek <krishna.vivek@gmail.com> wrote:
> I couldnt get a proper subject for the post but here is my question.
> Its regarding methods like
> attr_reader defined like below
> You can do this in ruby
>
> # file a.rb
> class A
>   call_this ("hello world")
>
>   def  call_this
>  ....
>   end
> end
>
>
> The A::call_this is called immediately after I run the script.Becuase I
> made the method print something and it printed it even though I hadnt
> instantiated an object of the class with new.
> What if the method uses some instance variables? wouldnt that be a
> problem because its called even before an object is created?My question
> is at what time during program execution are these methods called? If
> there are more than one classes in a file then whats the order ? is it
> defined by the language?
> My guess is that these are like the equivalent of static member
> variables in C, initialized before _main is called.?
> Hope to get some clarification on this
> vivek
>

Actually your code will generate an error. You can do this:

class Foo
  def self.bar
    puts 42
  end

  bar
end

This will work as the method bar exists and belongs to the class Foo,
not an instance of Foo. This will not work:

class Boo
  def hoo
    puts "Python is nice, but I like Ruby better :-)"
  end

  hoo      # this will raise a NoMethodError, unless hoo had been
defined further up the chain
end

Of course you can work around much of this with fun method_missing
maddness. In the particular case of attr_reader, they are actually
part of Module which is the superclass of Class, that is why you can
call them inside your class definitions -- they are methods available
in Class (and you are defining a Class).

pth