From: dblack@...
Date: 2006-03-12T12:49:57+09:00
Subject: Re: from Python to Ruby in 10 seconds

Hi --

On Sun, 12 Mar 2006, Bill Guindon wrote:

> On 3/11/06, Dave Burt <dave@burt.id.au> wrote:
>> I find Logan's answers accurate and complete, except for one, which is a
>> little complicated. Let me add a little to his answer.
>>
>> John M. Gabriele wrote:
>>>> - Python uses _foo, __bar, and __baz__ underscore notation
>>>> loosely for private references. Does Ruby have similar
>>>> notions of "privacy"?
>>
>> Logan Capaldo wrote:
>>> Method visibility can be controlled via the private, public, and
>>> protected key words. You can always get past these of  course by use  of
>>> #instance_eval for instance.
>>
>> In "foo.bar", bar is always a method, not a variable. What we call
>> attributes are methods that behave like attributes. "foo.bar = baz" calls a
>> method called bar=. We use attr_accessor, attr_reader and attr_writer to
>> create attributes with their own variables. For example, "class Foo;
>> attr_accessor :bar; end; foo = Foo.new"
>
> I found this a bit confusing.  Maybe....
> attr_accessor, attr_reader and attr_writer can be used to create
> attributes with their own variables.  They can also create the
> appropriate set/get methods for those (or other) variables.

If I can join the word-tweaking sweepstakes:  I don't think attributes
really have "their own" variables.  Give this:

   class C
     attr_accessor :x
   end

the methods x and x= have no unique claim to, or ownership of, @x.

Maybe one could say: The attr_* methods wrap instance variables in
simple, like-named getter and/or setter methods.  Given a pair of such
methods x and x=, wrapped around @x, objects of the class are said to
have an attribute "x".  Or something.

> The method names need to passed as symbols:
> class Foo
>  private :bar
> end

You can use a string too (private "bar").


David

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

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