From: Thomas Sawyer <transfire@...>
Date: 2009-02-01T05:03:20+09:00
Subject: Re: Object#singleton_class in Ruby 1.9?

Robert Dober wrote:
> On Fri, Jan 30, 2009 at 4:28 PM, Yukihiro Matsumoto <matz@ruby-lang.org> 
> wrote:
>> We still don't have consensus on the name.  eigenclass?
>> In that case, should we rename singleton_method to eigenmethod?
>>
>>                                                        matz.
> 
> Actually I am totally against it, in core that is. It would be nice to
> have a standard library extension for this, e.g. meta-ruby.
> I was really impressed about by David's keynote at Rubyconf. Just
> thought to share this thoughts in case I am not a minority.

You are against having a method altogether, you mean?

I take it because of the very nature singleton_methods / eigenmethods. 
And, I'm guessing, you prescribe to the idea that the only good way to 
the singleton "space" is to include modules into it, rather than 
defining methods directly. There was a blog post around somewhere to 
that effect. It was a good article. I wish I could dig it up now, but 
I'm not finding it. Perhaps someone else has the link? In any case, if 
that's what you mean, then I generally agree. That article was right, 
there rarely is a good reason to define methods directly into the 
singleton, one should be including a module with the methods defined in 
it instead. The only exception may be class-level methods, but even then 
using #extend deserves more merit.

Taking that idea to heart perhaps a reorientation on the matter is 
warranted.
Consider this form in place of the usual 'class << self':

  class X
    extend Module.new {
      ...
    }
  end

Not quite as elegant since we can't use do...end. But if #extend could 
take a block:

  class X
    extend do
      ...
    end
  end

Then the issue becomes transparent. Even for regular objects:

  obj.extend do
    ...
  end

This is not to say that a singleton_class/eigenclass method would never 
be of use, but it would certainly mitigate the need for it a great deal. 
(One might also take away from this that a better name for it, if it 
were given a method name, would be #extension, but I mention that only 
as an aside.)

T.
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