From: Stefano Crocco <stefano.crocco@...>
Date: 2008-06-30T04:19:30+09:00
Subject: Re: implicit vs explicit self in private methods

On Sunday 29 June 2008, dusty wrote:
> I'm trying to understand the difference between implicitly and
> explicitly calling a private method and am hoping someone could shed
> some light on this for me.
>
> class Tester
>   def public_hello_good
>     say_hello
>   end
>   def public_hello_bad
>     self.say_hello
>   end
>   private
>   def say_hello
>     "hello"
>   end
> end
>
> irb(main):001:0> require 'tester'
> => true
> irb(main):002:0> a = Tester.new
> => #<Tester:0x8c294>
> irb(main):003:0> a.public_hello_good
> => "hello"
> irb(main):004:0> a.public_hello_bad
> NoMethodError: private method `say_hello' called for #<Tester:0x8c294>
> 	from ./tester.rb:6:in `public_hello_bad'
> 	from (irb):4
> 	from :0
>
> What I'm wondering is why does this not work when I call
> self.say_hello, but does work when I call say_hello?  Since self is
> the receiver in both cases, it seems that they would both work.
>
> Anyone have any insight that they'd be willing to share on why it
> works like that?
>
> Thanks

It's at the same time quite simple and quite confusing. It's simple because 
the rule determining how a private method can be called is very short and 
clear: you can only call a private method using the implicit receiver. It's 
confusing because it seems natural to interpret the previous statement so that 
it reads: you can only call a private method if the receiver is equal (in the 
eql? sense) as the implicit receiver. However, this interpretation is wrong. 
The words "only using the implicit receiver" should be taken literaly: if a 
method is private, you can't call it using the dot notation 
(receiver.method_name), even when the implicit and the explicit receiver are 
the same thing.

I hope this helps

Stefano