From: dblack@...
Date: 2006-02-25T05:58:15+09:00
Subject: Re: Private methods - only available to oneself?

Hi --

On Sat, 25 Feb 2006, James Byrne wrote:

> Hal Fulton wrote:
>> Minkoo Seo wrote:
>>> Thanks, Erik. I'm afraid that I'm not a native English spearker, so
>>> sometimes it's not easy to express my own idea in exact English
>>> expression.
>>>
>>> Of course, I did look up the reference and found what instance_eval
>>> does when being called. What I tried to ask was, as you stated,
>>> "If we can do this, what's the purpose of 'protected' or 'private'?"
>>
>> 'private' is not like a locked door. It is like a sign saying "Do Not
>> Enter.'
>>
>> Or look at it this way: It makes it "more difficult" to access private
>> vars (so that you will know you shouldn't), but doesn't make it
>> impossible (in case you really, really need to).
>>
>>
>> Hal
>
> I do not understand why within the class definiton the Ruby interpreter
> distinguishes between implicit and explict calls to self.
>
> i.e
>
> Class Foo
>
> def foo_one
>  bar
> end
>
> def foo_two
>  self.bar
> end
>
> def bar
>  puts "In Bar"
> end
>
> private  :bar
>
> end
>
> f = Foo.new
>
> f.foo_one
> -> "In Bar"
>
> f.foo_two
> -> NoMethodError: private method `bar' called for
>
> This leads to the inference that self !=== <implicit self> which strikes
> me as decidedly odd.  Self is either always self or it is not and if not
> then what is it? Whether self is declared as the the receiver or left
> for the interpreter to contextually establish should make no difference
> to the effect of a private method.  Is this difference due to a parsing
> limitation or a purposeful design decision that serves some intent I
> cannot presently fathom?  If the latter, then what is the purpose served
> by this disticntion between an explicit and implicit self receiver?

I'm mostly guessing, but I imagine because it would be hard to
establish that exception to the rule, and the exception would serve no
purpose.  Also, I think of self as a *representation* of the current
object.  So when the interpreter sees:

   x

it doesn't literally stick "self" on the front; it just sends the
message to the current object.


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

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