[ruby-talk:02775] Re: More code browsing questions

Albert Wagner <[e-mail]> writes:

> Thanks again, Dave. I understand your example, but not the following
> code from ext/tk/lib/tkafter.rb:
> :
> require 'tk'
> 
> class TkAfter
>   include TkCore
>   extend TkCore

Ah - now you need the chapter I just wrote on classes and objects.

In Ruby, class definitions are executable code, not just lame old
declarations. So, while it is trundling through

  class TkAfter
    :
  end

Ruby is executing code. In this case, 'self' is actually set to
reference TkAfter, which is an object of type class.

  class TkAfter
    puts self.type
    puts self.name
  end

  => Class
  => TkAfter

The other thing to know is that a method called with no receiver has
an implicit receiver of 'self', so matz's Tk code is equivalent to

  class TkAfter
    [self.]include TkCore
    self.extend  TkCore

  end

(the reason for the [self.] is that 'include' is a private method, and 
can't in reality be called with a receiver).

So, what does this incantation do? Let's try it.

  module TkCore
    def tclMe
      puts "Hee Hee!"
    end
  end

  class TkAfter
    include TkCore
    extend  TkCore
  end

  tka = TkAfter.new
  tka.tclMe           # => Hee Hee!

  TkAfter::tclMe      # => Hee Hee!


So, by including the module, you make its methods available as
instance methods. By extending yourself with it, you make its methods
available as class methods.



Dave