# I Broke Ruby (i.e. Missing the Brutally Obvious)

**URL:** <https://www.ruby-forum.com/t/i-broke-ruby-i-e-missing-the-brutally-obvious/53412>\
**Category:** Ruby\
**Created:** [February 4, 2006, 9:44am UTC](https://www.ruby-forum.com/t/i-broke-ruby-i-e-missing-the-brutally-obvious/53412 "2006-02-04T09:44:08Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![bluetrust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@bluetrust](https://www.ruby-forum.com/u/bluetrust)\
**Post date:** [February 4, 2006, 9:44am UTC](https://www.ruby-forum.com/t/i-broke-ruby-i-e-missing-the-brutally-obvious/53412/1 "2006-02-04T09:44:08Z")

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It’s been yet another late Friday. It’s practically a lifestyle by this  
point. (I’m glad my wife understands.) So anyway, things were going  
fine until I tried to get two ruby files to require each other.  
Suddenly the class defined in the first file was considered  
“uninitialized.”

Here’s some code demonstrating the error:

Type into IRB:  
require “a”  
NameError: uninitialized constant A  
from ./b.rb:3  
from ./a.rb:1  
from (irb):3

Place these files in the same directory you call irb in:

File a.rb  
require “b”

```
class A < Array
  # Do nothing
end

```

File b.rb  
require “a”

```
class B < A
  # Do nothing
end

```

Where’s the brutally obvious mistake I made? Why would A be an  
uninitialized constant?

---

<div class="post-metadata">

**Author:** ![bluetrust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@bluetrust](https://www.ruby-forum.com/u/bluetrust)\
**Post date:** [February 4, 2006, 10:40am UTC](https://www.ruby-forum.com/t/i-broke-ruby-i-e-missing-the-brutally-obvious/53412/2 "2006-02-04T10:40:12Z")

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Michael J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

> ```
> class B < A
> # Do nothing
> end
> 
> ```
> 
> Where’s the brutally obvious mistake I made? Why would A be an  
> uninitialized constant?

Because it hasn’t been defined when “class B \< A” is evaluated.  
Here’s what happens, step by step:

- irb evaluates: require “a”
  - ruby parses the ‘a.rb’ file into an internal representation, doing  
syntax checking along the way
  - ruby evaluates the first expression: require “b”
    - ruby parses the ‘b.rb’ file into an internal representation,  
doing syntax checking along the way
    - ruby evaluates the first expression: require “a”. As ‘a.rb’ has  
already been required, this does effectively nothing (see `ri  
require’).
    - ruby evaluates the next expression: class B \< A … end. As A  
is not defined, ruby raises the exception you see.

Why does ‘a.rb’ require ‘b.rb’ ? Circular requires are a bad thing.  
You’ll need to break it up.

One option is to just have the toplevel file just have a whole  
sequence of requires, and have each source file define what it needs  
to without messing around with any requires whatsoever.

Hope this helps.

---

<div class="post-metadata">

**Author:** ![bluetrust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@bluetrust](https://www.ruby-forum.com/u/bluetrust)\
**Post date:** [February 5, 2006, 11:59pm UTC](https://www.ruby-forum.com/t/i-broke-ruby-i-e-missing-the-brutally-obvious/53412/3 "2006-02-05T23:59:25Z")

</div>

George O. wrote:

> Michael J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:
> 
> > ```
> > class B < A
> > # Do nothing
> > end
> > 
> > ```
> > 
> > Where’s the brutally obvious mistake I made? Why would A be an  
> > uninitialized constant?
> 
> Because it hasn’t been defined when “class B \< A” is evaluated.  
> Here’s what happens, step by step:
> 
> - irb evaluates: require “a”
> - ruby parses the ‘a.rb’ file into an internal representation, doing  
> syntax checking along the way
> - ruby evaluates the first expression: require “b”
> - ruby parses the ‘b.rb’ file into an internal representation,  
> doing syntax checking along the way
> - ruby evaluates the first expression: require “a”. As ‘a.rb’ has  
> already been required, this does effectively nothing (see `ri  
> require’).
> - ruby evaluates the next expression: class B \< A … end. As A  
> is not defined, ruby raises the exception you see.
> 
> Why does ‘a.rb’ require ‘b.rb’ ? Circular requires are a bad thing.  
> You’ll need to break it up.
> 
> One option is to just have the toplevel file just have a whole  
> sequence of requires, and have each source file define what it needs  
> to without messing around with any requires whatsoever.
> 
> Hope this helps.

Thanks for your help, George. That’s really interesting how the ruby  
parser works.

If instead I did, require “b” in irb, it would have worked because the  
following sequence would have happened:

1. Parse b.rb until hitting the line: require “a”
2. Parse a.rb (in the process, learning about class A)
3. Continue parsing b.rb
4. Class B’s definition (subclassed to A) now makes sense to the parser  
and everything works.

Crazy stuff. It makes me want to write a programming language.

In the end, after reading your post, I decided to move class B into the  
bottom of a.rb and my unit tests passed. It just seemed simpler than  
creating a file that just requires all the different class files.

(Thanks again for taking the time to explain how the parser worked)