From: Phrogz <gavin@...>
Date: 2007-03-28T02:30:04+09:00
Subject: Re: How do I implement the Unix 'tee' function for $stdout?

On Mar 27, 10:55 am, Larry Fast <l...@mdsi.ca> wrote:
> Erik Veenstra wrote:
> >  ["$stdout", "$stderr"].each do |std|
> >    io           = eval(std)
> >    old_write    = io.method(:write)
>
> >    class << io
> >      self
> >    end.module_eval do
>
> >        old_write.call(text)
[snip]
> Last question: what does "self" do on the line below "class << io"

  >> class Rectangle; end
  => nil

  >> r = Rectangle.new
  => #<Rectangle:0x2c8bfe8>

  >> class << r; self; end
  => #<Class:#<Rectangle:0x2c8bfe8>>

The last expression in a block is the value of that block. In the
above, 'self' is used to 'return' the singleton class that was opened
with "class << io".

Various libraries have code like:
  class Object
    def singleton_class
      class << self
        self
      end
    end
  end
abstracting the somewhat odd notation. With this, the original code
could be written as:

io.singleton_class.module_eval ...