From: Justin Collins <justincollins@...>
Date: 2010-01-18T19:00:22+09:00
Subject: Re: Newbie needs help getting started

Cary Swoveland wrote:
> I have just written the code for my first Ruby program, one that finds
> the shortest path from start to finish in a maze.  All i/o is through
> files and a terminal.  I have now turned to debugging it.  To help me, I
> have the books, "The Ruby Programming Language" and "Ruby Cookbook", and
> of course vast internet resources.  I'm using Ruby 1.8.7 on a MacBook. I
> need a few answers to help me get started.
>
> 1. Is this the normal way to debug a program: with a terminal window
> open, save changes to the x.rb file in an editor, and enter
>
> ruby "filename" args
>
> in the terminal? (Presumable, using a Ruby IDE is another alternative.
> I've also noted how irb works.) 

Yes, this is a pretty typical work sequence.


> If "yes", does the execution begin with
> the first statement that is outside a class definition (as there seems
> to be nothing comparable to C's main(), for example)?
>   

Actually, execution begins with the very first line of non-comment code. 
Even class definitions are actually executable code. Try putting a 
"puts" somewhere in a class definition, but outside of a method.

> 2. Suppose I've defined two classes, C1 and C2, a "main" program and
> some methods that are outside class definitions.  Assume there is a
> statement
>
> c1 = C1.new
>
> in a class C2 method and
>
> c2 = c2.new
>
> in a method outside the two classes.  In the file containing my code,
> maze_problem.rb, do these blocks of code have to be placed in any
> particular order?
>   

Consider what I said above about code execution. Beyond that, whether or 
not the method outside of any classes will work depends on when it is 
called, rather than when it is defined.

> 3. I ran
>
> ruby maze_problem.rb
>
> in the terminal and got the following error message:
>
> undefined method `[]=' for nil:NilClass
>
> with no reference to where in maze_problem.rb the problem occurred.  How
> do I go about finding the source of this error?
>
> Many thanks.
>
> Cary
>   

Are you sure that is the entire error message?
In any case, look for a place where you are setting an element on a 
variable using a[blah] = something.

-Justin