From: Bill Atkins <batkins57@...>
Date: 2004-10-06T23:23:12+09:00
Subject: Re: quality of error messages

On Wed, 6 Oct 2004 22:48:49 +0900, Joachim Wuttke
<joachim_wuttke@ph.tum.de> wrote:
> Hi Ruby developers,
> 
>    after spending some time with Perl and Python, I am
> currently exploring Ruby. While I am quite enthusiastic
> about some of its features, I am increasingly preocuppied
> about the difficulties to localize errors.
> 
>    Example 1: missing "end" in <last-line-of-code>
> -> I forget to close a "class" or a "do" or a "if" block -
> but which one ? Shouldn't the system be able to name
> possible locations of unclosed block openings ?

From what I understand, it's pretty difficult for Ruby (or any other
compiler) to figure out where the improperly-ended block began.  Using
ruby-mode or some other automatic indenting system can help you spot
these errors.

Consider the following C code:

int main() {
  if(1) {
    // do something

  int var = 34;
  while(var < 10) {
    var--;
  }
}

gcc gives a similar message ("syntax error at end of input"). 
Obviously, the bracket for the if statement was never closed, but it's
difficult for a compiler to tell where it was supposed to end.  (For
example, is the bracket closing the while meant to close the if
statement?)


>    Example 2: NoMethodError: undefined method.
> -> Wrong, I defined the method. I just forgot to
> include it in the attr_reader list. The system
> shouldn't mislead me.

Hmm, you shouldn't be listing methods you've defined in an attr list. 
the attr_* methods define getter and/or setter methods for the names
you pass to them.

Maybe you mean that you haven't declared an attr for some instance
variable and running object.variable gives you a NoMethodError.  In
that case, remember that Ruby has no way to know the object.variable
is an attr_reader as opposed to a regular, user-defined method.  Just
keep in mind that all accessors are just methods and then the error
message will probably seem more informative.

> 
>    Developers, do you share my opinion that this would
> be worth working upon ? I would really like to hear that
> error messages will improve in future versions of the
> interpreter.
> 
>    Once I open a Ruby/Tk session, error messages are
> redirected to an annoying popup window. Can I disable
> this behavior ? I would prefer to see errors in stdout,
> even when I am running a GUI.
> 
>    Regards, Joachim
> 
>