From: Jos Backus <jos@...>
Date: 2007-01-20T02:17:40+09:00
Subject: Re: Scoping and locating definitions

    Hi Eric,

On Fri, Jan 19, 2007 at 05:03:16PM +0900, Eric Hodel wrote:
> On Jan 18, 2007, at 15:53, Jos Backus wrote:
> 
> >Consider the following:
> >
> >lizzy:~% cat r
> >require 'lib'
> ># from 'lib' import 'Foo'
> >
> >f = Foo.new("string")
> >p f.bar
> >
> >p 'abc'.rot13
> >lizzy:~% cat lib.rb
> >class String
> >  def rot13
> >    tr 'A-Za-z', 'N-ZA-Mn-za-m'
> >  end
> >end
> >
> >class Foo
> >  def initialize(s)
> >    @s = s
> >  end
> >
> >  def bar
> >    @s.rot13
> >  end
> >end
> >lizzy:~% ruby r
> >"fgevat"
> >"nop"
> >lizzy:~%
> >
> >What if I wanted String#rot13 to _not_ be visible in file  
> >`r' (because I
> >didn't ask for it)?  How do I contain the change to String to  
> >lib.rb only?
> 
> Currently you can't.
 
Right. I think it's important that the language supports this though.
`require' can pollute the caller's code in uncontrollable ways, and it would
be very useful to have control over this behavior.

> >Or perhaps to Foo?
> 
> Define Foo#rot13
> 
> >On a related note: how does one go about finding _where_  
> >String#rot13 was
> >defined? One possible way would be for .methods to return an Array of
> >BoundMethods instead of Strings and have file and linenumber  
> >information be
> >part of BoundMethod (if possible).
> >
> >Thoughts?
> 
> grep?
 
Heh. The interpreter knows where it saw the most recent method definition; why
not make this information available?

Python, with its closed classes, doesn't have this "issue" because method
definitions only live in one place per class. A colleague at work considers
the fact that it's hard to find out where methods are defined a weakness, and
I'd like to present him with a better answer than `grep'. It sounds like some
more introspection could solve this "issue".

Thanks,
-- 
Jos Backus
jos at catnook.com