From: Jim Cochrane <allergic-to-spam@...>
Date: 2006-07-23T06:40:07+09:00
Subject: Re: Self, looking for a good summary explanation

On 2006-07-22, Dark Ambient <sambient@gmail.com> wrote:
> Sorry, because I have the books and have / continuing to  read, just
> trying to wrap myself around one aspect of "self".
>
> My understanding is that 'self' changes amongst objects depending on
> program code execution.  This I get (at some level). what I don't
> understand is why are some objects named self outright and does it
> actually matter if you named something self or something else ?

self is not a variable name - It's a key word that refers to the current
object (the object to which the currently executing code in question
belongs).  It's often not needed - e.g.:

class A

	def b
		# ...
	end

	def c
		self.b
	end

	def d
		b
	end

end

both 'c' and 'd' do exactly the same thing, call b on the current object,
using different syntax.  However, sometimes self is necessary - e.g.:

x.rb:

class X
	def method1(some_object)
		some_object.do_something_or_other(self)  # Pass my'self' - me, the
                                                 # current object as an arg.
	end
	# ...
end

y.rb:

require 'x'

class Y
	def do_work
		x = X.new
		x.method1(self)      # Again, pass my'self'.
	end

	def do_something_or_other(client)
		puts "doing something with #{client}"
	end
end

test-y:


#!/usr/bin/env ruby

require 'y'

y = Y.new
y.do_work




Note that 'self' is used twice in the above example.  (This is the only
way, as far as I know, to pass a reference to "the current object" in
these method calls, so 'self' is a necessary keyword.  All OO languages
have such a keyword - e.g., 'this' in C++ and Java, 'Current' in Eiffel,
'self' in Python, Ruby, and, I think, Smalltalk.)  It doesn't do anything
useful, since it's just a demo, but a serious program that uses 'self'
will need it to do something useful, of course.