From: Florian Frank <flori@...>
Date: 2004-10-07T00:29:12+09:00
Subject: Re: quality of error messages


On 06.10.2004, at 16:49, Joachim Wuttke wrote:
> But:
> (1) the system should tell me which method in the above
> chain causes the problem

Actually it does.

> (2) as a naive programmer, with a background in other languages,
> I do not think of pos as method. I think of it as variable.
> Once the system does not find a method, it could check whether
> there is a local variable of same name, and then print out
> an error message like
>    "no method 'pos', no read access to local variable 'pos'".

You should think of it as a method. That's called the Uniform Access 
Principle. It's true that almost all of the so called OOP languages get 
it wrong, but that doesn't mean that Ruby should join them. Consider 
that you change the implementation of your class and "pos" isn't a 
variable (field) anymore but computed instead. In some other languages 
you now have to change all the client code that directly accesses the 
variable. That's exactly the opposite of data hiding and encapsulation 
of state.

Florian Frank