From: dblack@...
Date: 2006-10-20T10:51:30+09:00
Subject: Re: String not enumerable, what about IO?

Hi --

On Fri, 20 Oct 2006, Michael Selig wrote:

> I am fairly new to ruby, and I have just started listening to this mailing
> list, so please don't flame me too much if I get things wrong!
>
> ----- Original Message -----
> From: "Mauricio Fernandez" <mfp@acm.org>
>>
>> What about:
>> * defining String#to_enum, which would accept an argument (:lines, :chars
> or
>>   :bytes) defaulting to :lines. Note that right now (in HEAD)
> "foo".to_enum
>>   ends up using Kernel#to_enum, raising a NameError (undefined #each for
> class
>>   String).
>> * making  str.lines (chars, bytes) equivalent to
>>   str.to_enum(:lines).to_a  (respectively :chars, :bytes)
>
> Though I have never used it, doesn't Ruby already have something (admitedly
> rather long-winded) to do this called Enumerable::Enumerator?
>
> I would also like to add my 2 cents worth to this discussion.
>
> I have found Enumerables rather confusing, as there are many variants of
> "each" in a number of different classes.

That's sort of the point :-)  All of the other enumerable methods --
select, reject, inject, etc. -- are built on top of each.  If you
define an each method for your class and mix in Enumerable, you get
all the enumerable methods for free.

> What I would prefer (and this would probably be a major change to the
> implementation) is to be able to treat ALL enumerable classes as Arrays. In
> other words, I'd like to suggest that Array and Enumerable effectively be
> the same thing, and that "Array" would be the superclass instead of
> "Enumerable".

Enumerable isn't a superclass; it's a module.  Don't forget you can
mix it in to your own classes, so it's not just a matter of the
behavior of Ruby core classes that are Enumerable.

Also, in some respects Array is the common currency of Enumerables, in
the sense that a lot of Enumerable methods return arrays.  But that
doesn't mean that Array itself is more Enumerable, so to speak, than
other Enumerable classes.

> Of course this would only be on the surface - underneath the implementation
> of each would probably have to be different for efficiency.
>
> Thius would add possibly useless methods like Range#[], but why not?

Because they're useless.  I'd like to see things refactored a bit in
Enumerable and the related classes (e.g., push each_with_index down
into the individual classes), but I would not like to see useless
methods.

> Most enumerable classes are ordered, so the Array#[] method would
> work fine.  Hashes are an exception, and obviously Hash#[] would be
> different.

I'm not getting a clear picture of what you're proposing.  How would I
write an Enumerable class?  It sounds like I'd have to subclass Array,
which definitely isn't equivalent to what Enumerable offers.


David

-- 
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org