From: dblack@...
Date: 2002-11-20T09:53:00+09:00
Subject: Re: Learning Ruby

Hi --

On Wed, 20 Nov 2002, Daniel Carrera wrote:

> Hi,
>
> I am a Perl hacker trying to get to know Ruby.  I have two questions:

Welcome :-)

Partial response:

> I noticed that Ruby doesn't let me use functions until after I define
> them (unlike Perl).  Why is that?  I want to have the freedom to define
> the functions anywhere.

Pretty much everything happens in lexical sequence in Ruby, so if you
ask for a method to be called, it has to exist.  As a corollary, you
can also redefine methods:

  def my_method
    puts "hi"
  end

  my_method   # hi

  def my_method
    puts "hello"
  end

  my_method   # hello

This is a pretty dinky example -- but you can see that having a call
to my_method before any version of it was defined wouldn't make sense.

Nor is it possible to do some kind of lookahead where the last
definition of a method is known in advance.  Method definition may be
conditional on runtime state, so there's no way to anticipate which
definition is "last".

Another way to look at it is: a Ruby object responds to messages
(i.e., method names), and the set of messages it can respond to is
subject to change during the life of the object.  Therefore, there's
no way to do method existence lookahead.  The transaction -- the
method call -- always succeeds or fails based on the capacities of the
object at the time of the call.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav