From: Todd Benson <caduceass@...>
Date: 2008-03-08T05:20:08+09:00
Subject: Re: instance_eval and class_eval - names got mixed up?

On Fri, Mar 7, 2008 at 2:06 PM, Bharat Ruparel <bruparel@mercury.com> wrote:
> Going through the Ruby Programming Language text Chapter 8 Reflection
>  and MetaProgramming.  Section 8.2.2 on page 270.
>
>  The following paragraph has me puzzled:
>
>  "Note the subtle but crucial difference between instance_eval and
>  class_eval when the code being evaluated contains a method definition.
>  instance_eval defines singleton methods of the object (and this results
>  in class methods when it is called on a class object).  class_eval
>  defines regular instance methods."
>
>  Is this not supposed to be the other way around?  instance_eval should
>  define instance methods and class_eval should define class methods.  Is
>  there a catch here?  Ruby is supposed to be following principle of least
>  surprise.  I must say I am surprised here, or there is something quite
>  profound that I don't get.
>
>  Bharat

It's the use of the word "instance" here that causes the problem.
Singleton methods are specific to a single instance of an object.  An
instance method refers to a method that's available to _every_
instance of a class upon their creation.  Maybe it should be
singleton_eval and instance_eval, but, see, that doesn't really make
sense, because that would imply eval being used within the singleton
class of the object.  One of those meta-programming language
work-arounds I guess.

Todd