Ruby error messages

Hi there,

Is the meaning of the ruby error messages defined anywhere? E.g. I get
something like:

NameError: uninitialized constant Blah

and maybe you'll tell me it's self explanatory, but it would be nice to
look through a list of errors and read more about what they mean. I
searched the web and asked on ruby-lang irc channel but haven't turned
up anything yet.

Many thanks in advance.

···

SAM

Sam Joseph wrote:

Hi there,

Is the meaning of the ruby error messages defined anywhere? E.g. I get
something like:

NameError: uninitialized constant Blah

and maybe you'll tell me it's self explanatory, but it would be nice
to look through a list of errors and read more about what they mean. I
searched the web and asked on ruby-lang irc channel but haven't turned
up anything yet.

As far as I know there is no such comprehensive list (note, I may be wrong
here). But closely looking at the exception stack trace and the code it
points to you usually see what's wrong very fast.

Kind regards

    robert

NameError: uninitialized constant Blah

irb(main):002:0> x = My_case_is_wrong
NameError: uninitialized constant My_case_is_wrong
        from (irb):2
irb(main):003:0>

usually,
grep -r Blah you_program_dir
is make clear the situation.

Sounds like a decent wiki page.

What it means is that something Ruby considers a constant is being used without being initialised, which I suppose is obvious.

The less-obvious bit is "something Ruby considers a constant" which is "an identifier that starts with an uppercase letter". All class and module names, for instance. (Forgive me if that's a little amorphous - I don't have a language grammar to poke through for the actual definition).

So, for this error, I would look for typos, particularly in assignment statements (as one poster mentioned), but also in class definitions - maybe you defined your class as "Balh" when you meant "Blah". For particularly tricky cases, you can get a list of constants via 'Module.constants'.

matthew smillie.

···

On Nov 24, 2005, at 8:01, Sam Joseph wrote:

Hi there,

Is the meaning of the ruby error messages defined anywhere? E.g. I get
something like:

NameError: uninitialized constant Blah

and maybe you'll tell me it's self explanatory, but it would be nice to
look through a list of errors and read more about what they mean. I
searched the web and asked on ruby-lang irc channel but haven't turned
up anything yet.

Thanks Robert and Yuri,

As a ruby newbie I'm finding that I'm getting a little stuck. I've been programming in Java/C like languages for about 15 years, so maybe I'm just having trouble getting used to the brave new world, so perhaps you'll bear with me while I take you through some details.

I really like ruby but I'm finding it hard to get to the bottom of things when I do get errors.

My current situation involves a module called Gruff. I've mailed my problems to the gruff forums on rubyforge, and we're working on it there, however I'd really like to be able to help solve the problem myself.

I've downloaded gruff and rmagick using gems, and I'm trying a gruff code sample in irb (I previously tried an rmagick sample and that works):

require 'rubygems'
require 'gruff'

g = Gruff::Line.new

require 'rubygems' returns a fail, and require 'gruff' gives an error, but I can get it to just return false if I comment out the relevant line of code in the gruff source.

Anyhow, when I type g = Gruff::Line.new I get the this error:

NameError: uninitialized constant Gruff

which I presume is telling me that we have failed to pull in the gruff module - adjusting the capitalization is no help:

irb(main):004:0> g = gruff::Line.new
NameError: undefined local variable or method `gruff' for #<Object:0x2959258>
        from (irb):4

The thing is I'm stuck as to how to proceed from here - is there some way for me to interogate the system so I can find out why the require 'gruff' is failing?

As I understand it my path is set up fine:

irb(main):005:0> $:
=> ["d:/ruby/lib/ruby/gems/1.8/gems/RMagick-win32-1.9.2-mswin32/bin", "d:/ruby/lib/ruby/ge
ms/1.8/gems/RMagick-win32-1.9.2-mswin32/lib", "d:/ruby/lib/ruby/gems/1.8/gems/gruff-0.0.6/
bin", "d:/ruby/lib/ruby/gems/1.8/gems/gruff-0.0.6/lib", "d:/ruby/lib/ruby/site_ruby/1.8",
"d:/ruby/lib/ruby/site_ruby/1.8/i386-msvcrt", "d:/ruby/lib/ruby/site_ruby", "d:/ruby/lib/r
uby/1.8", "d:/ruby/lib/ruby/1.8/i386-mswin32", "."]

i.e. i get all the above after entering the require commands, despite the fact that they return failures.

hmm, so actually writing all this out helped - as I just fixed the problem. It seems that I needed to restart irb each time I made modifications to the source code in order to see the continuing errors being generated after my modifications.

I was confused beacause after throwing an error once, a repeat call to require would just return false, without any error message. By restarting irb and seeing the addtional errors, I commented out a load of undef_method calls in rmagick.rb and now it all works.

Sometimes you just need to be able to explain these things to someone :slight_smile:

Many thanks for your input

SAM

Robert Klemme wrote:

As far as I know there is no such comprehensive list (note, I may be wrong
here). But closely looking at the exception stack trace and the code it
points to you usually see what's wrong very fast.

Yuri Kozlov wrote:

···

NameError: uninitialized constant Blah
   
irb(main):002:0> x = My_case_is_wrong
NameError: uninitialized constant My_case_is_wrong
       from (irb):2
irb(main):003:0>

usually, grep -r Blah you_program_dir
is make clear the situation.

Find Gruff lib. There is a base.rb file.

In
-------------8<-------8<-------------
1. begin
2. require 'rmagick'
3. rescue LoadError
4. require 'RMagick' # capitalized on Windows
5. end

-------------8<-------8<-------------
comment out lines 1-3 and 5. Gruff does not deal good with "requre" on
Win.

Hope this helps you.

Pavel

···

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