From: 7stud -- <bbxx789_05ss@...>
Date: 2009-09-19T14:58:15+09:00
Subject: Re: Mucking about with dynamically adding methods to objects

7stud -- wrote:
> 
> define_method() to the rescue:
> 
>   def talkify(obj, str)
>     obj_singleton = get_singleton_class(obj)
> 
>     obj_singleton.class_eval do
> 
>       define_method("talk") do
>         puts str
>       end
> 
>     end
> 
> Neither of the blocks used with class_eva() or define_method() creates a 
> new scope, so code inside them can make use of variables defined in the 
> surrounding scope.
> 

Hmm...I've decided that I find that explanation totally unsatisfying. 
If define_method() really created a method, then inside the created 
method str would be undefined.  Since str isn't undefined when the talk 
'method' is called, define_method() must really create a closure 
somewhere along the line, i.e. something like a Proc object. Maybe 
define_method() creates a method that calls a Proc object?  For 
instance, something like this:

def talk
   a_proc.call
end

where a_proc is created like this:

a_proc = Proc.new {puts str}

which forms a closure, so all the variables in scope at the time a_proc 
was created can be referenced inside a_proc.
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