From: James Edward Gray II <james@...>
Date: 2006-08-12T01:47:34+09:00
Subject: Re: instance_eval vs. class_eval context

On Aug 11, 2006, at 11:14 AM, ts wrote:

>>>>>> "A" == Arnaud Bergeron <abergeron@gmail.com> writes:
>
> A> No.  In case of instance_eval you will be in the class, and in the
> A> case of (class|module)_eval you will be in the class of the class
> A> (which is Class) [Hurray for multiple meanings to a word!]
>
>  no, not really. ruby use self and internally ruby_class which give it
>  where it can define method when it find keyword like 'def',  
> 'alias', ...
>
>  With obj.instance_eval ruby will make
>    * self = obj , ruby_class = obj singleton class
>
>  This mean that inside instance_eval it will define singleton method
>
>  #instance_eval work with any object, but a class is a little special
>  because it can be seen as an object or as a class. This is why
>  #module_eval, #class_eval exist.
>
>  With obj.class_eval ruby will make
>
>   * self = obj, ruby_class = obj
>
>  This mean that inside class_eval ruby will define instance method.
>
>  One way to see it
>
> moulon% ruby -e 'class A; end; A.instance_eval{ p self; def a()  
> puts "A::a" end}; A.a'
> A
> A::a
> moulon%
>
> moulon% ruby -e 'class A; end; A.class_eval{ p self; def a() puts  
> "A#a" end}; A.new.a'
> A
> A#a
> moulon%

I've always had trouble understanding this and for some reason this  
is the email that finally clicked all the pieces into place for me.   
Thanks Guy!

James Edward Gray II