From: Martin DeMello <martindemello@...>
Date: 2006-11-22T20:15:40+09:00
Subject: Re: Bug in ruby?

On 11/21/06, AliasX Neo <kamipride102@gmail.com> wrote:

>         istart = string.index(starting) + starting.length
[...]

> undefined method `+' for nil:NilClass

Other people have said this, but just to put it explicitly:

Ruby has a message-passing object model - every operation consists of
a message sent to an object. Thus, there are no symmetrical operations
- even binary operations like + translate internally to one object
being sent to the other as part of a "+" message. Indeed, you could
even write the above as

istart = string.index.starting.+(starting.length)

to make it explicit that there's a method call going on under the hood.

One consequence of this is that when an exception or error is thrown,
it is thrown from the context of the receiving object. Thus "undefined
method `+' for nil:NilClass" means you have attempted to call
nil.+(something), not something.+(nil). That should help greatly in
debugging stuff.

martin