From: Mark Hubbart <discordantus@...>
Date: 2005-05-16T09:25:23+09:00
Subject: Re: Visibility and the "self" receiver

On 5/15/05, M. Maniak <skull2crush@hotmail.com> wrote:
> Hello,
> 
> I'm new to Ruby (coming from Java) and puzzled
> by the behaviour of "self" when defining a private method:

try:

> -->Snip
> class TestClass
> 
>          def initialize(args)
>                  @myString = args
>                  print()
>          end
> 
>          private
>          def print()
>                  puts @myString
>          end
> end
> -->Snip

... which should work.

> This produces a NameError when instantiated/executed.
> Without reference to itself (without "self") everything works...
> 
> I guess print() is then treated as a function and not as
> a method (whatever that means in OOP -> maybe no return value).
> 
> I know that in Java "this" is a somehow comparable reference
> with "self" in Ruby and denotes the actual object. I use it
> quite often...
> 
> Has anyone an explanation about this specific behaviour (I know
> it's not a bug)? Maybe I don't get the principle of "private"
> or Visibility in general in Ruby.

Private methods can only be called without an explicit receiver. This
means that they can only be called when the implicit receiver is
"self", and no receiver is specified:

class A
  private
  def a() :a end
end

A.new.a  #==> error, a is private and called with an explicit receiver.
A.new.instance_eval do  #==> changes self to A.new for this block
  self.a  #==> error, explicit receiver
  a       #==> no error, implicit receiver is self
end

HTH,
Mark

> Thank you very much for a hint.
> 
> Greets,
> M. Maniak
> 
>