From: "David A. Black" <dblack@...>
Date: 2009-07-15T05:35:41+09:00
Subject: Re: Twelve rules of Ruby

Hi --

On Wed, 15 Jul 2009, Ryan Davis wrote:

>
> On Jul 14, 2009, at 06:16 , David A. Black wrote:
>
>> Not sure why they wrapped weirdly (at least on my screen), but here's
>> a correctly-wrapped version, I hope.
>
> Rick did a very good job with some of the philosophical wanking but I thought 
> I'd expand a bit on David's list... I have to be a pedant now and then :)
>
> (please note, I'm still pre-caffeine... I'm sure I missed something in the 
> editing phase)
>
>> 1. Classes are objects.
>
> I prefer to tell my students: EVERYTHING is an object, even classes.
>
> I think it conveys the ontology a bit better.

Well -- either one is shorthand, in the sense that when actually
teaching the stuff, much more than one sentence is required :-)

>> 2. Objects don't "have" methods; they have the intelligence to resolve
>>  messages by looking for methods along their class/module lookup
>>  path.
>
> See #1. Classes, modules, and their anonymous kin _have_ methods.

Of course. Otherwise there wouldn't be much point looking for a method
along a lookup path of them :-) That's really the point of the "has"
thing: objects don't define or own the methods to which they have
access. At the very least, ownership is class-mediated, including as
between a class object and its own singleton class.

(I know the whole singleton class thing is an implementation decision,
but, at least for now, it's a decision, rather than an incidental
detail.)

>> 3. Every instance variable you ever see in any Ruby program belongs to
>>  whatever object "self" is at that moment, without exception. (Which
>>  is one reason that understanding how "self" gets assigned is
>>  absolutely vital.)
>> 4. A code block is a syntactic construct, not an object.
>
> See #1. EVERYTHING is an object, even blocks.

I don't consider blocks or argument lists to be objects.

>> 5. Class variables are not class variables, in the sense of belonging
>>  to a particular class. They are class hierarchy variables.
>
> I know what you're getting at, but it might be worth having the contrast of 
> class instance variables in there so others understand too.

Do cut me some slack :-) I really wasn't trying to write a tutorial --
just a list of very succinct, suggestive, almost epigrammatic points.


David

-- 
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