# Weird class-loading issue (or maybe a problem with define\_me

**URL:** <https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558>\
**Category:** Ruby\
**Created:** [May 15, 2006, 5:20pm UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558 "2006-05-15T17:20:08Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 15, 2006, 5:20pm UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558/1 "2006-05-15T17:20:08Z")

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I’m working on an app and having a strange class loading problem.  
I’ve extracted it to the most basic code possible.

# foo.rb

require “bar”  
class Foo  
FOO = “foo”  
end

# bar.rb

require “foo”  
class Bar  
def self.set\_foo(val)  
define\_method(:foo) { val }  
end  
end

class FooBar \< Bar  
set\_foo Foo::FOO  
end

This works fine if I include bar.rb first:  
baggio:~/work/test pergesu$ irb  
irb(main):001:0\> require “bar”  
=\> true

but it blows up if I do foo.rb:  
irb(main):001:0\> require “foo”  
NameError: uninitialized constant FooBar::Foo  
from ./bar.rb:10  
from ./foo.rb:1  
from (irb):1

What’s even more strange to me is that the FooBar class has no problem  
accessing Foo::FOO from within a method, either class or instance:  
class FooBar \< Bar  
def foo; Foo::FOO; end  
def self.class\_foo; Foo::FOO; end  
end

irb(main):001:0\> require “foo”  
=\> true  
irb(main):002:0\> FooBar.new.foo  
=\> “foo”  
irb(main):003:0\> FooBar.class\_foo  
=\> “foo”

I’ve also moved self.class\_foo into the Bar superclass, and there were  
no problems. The only issue that pops up then is when I write a class  
method in Bar that ends up calling define\_method passing in a constant  
from the other file. It only happens when I require “foo”, but  
require “bar” works fine.

Can anyone tell me what’s going on here? I really don’t understand  
it. Also I’ve foundt that my program works if I require “bar” before  
everything…but I don’t like that solution. Most classes don’t even  
know that that file ever gets required, so it feels ugly that I’d have  
to require it at the beginning of every file I use.

Pat

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 15, 2006, 5:29pm UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558/2 "2006-05-15T17:29:23Z")

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On 5/15/06, Pat M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> I’m working on an app and having a strange class loading problem.  
> I’ve extracted it to the most basic code possible.

Change this:

> # foo.rb
> 
> require “bar”  
> class Foo  
> FOO = “foo”  
> end

to this:

# foo.rb

class Foo  
FOO = “foo”  
end  
require “bar”

Better yet, get rid of your circular dependency.

FooBar should be defined in a third file that requires foo.rb and  
bar.rb.

-austin

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 15, 2006, 6:07pm UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558/3 "2006-05-15T18:07:27Z")

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On 5/15/06, Austin Z. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> to this:
> 
> # foo.rb
> 
> class Foo  
> FOO = “foo”  
> end  
> require “bar”

I can’t, because some of the methods in the Foo class call Bar methods.

> Better yet, get rid of your circular dependency.
> 
> FooBar should be defined in a third file that requires foo.rb and bar.rb.

I’m not sure how that fixes anything. Foo has to create some Bar  
objects, and Bar has to have access to some of the Foo constants. I  
didn’t talk about that in my initial post, but each class interacts  
with each other.

Pat

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 15, 2006, 6:20pm UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558/4 "2006-05-15T18:20:35Z")

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On Tue, 16 May 2006, Pat M. wrote:

> I’m not sure how that fixes anything. Foo has to create some Bar  
> objects, and Bar has to have access to some of the Foo constants. I  
> didn’t talk about that in my initial post, but each class interacts  
> with each other.
> 
> Pat

a setup like this will give you that

harp:~ \> cat foo\_constants.rb  
module FooConstants  
FOO = 42  
end

harp:~ \> cat foo.rb  
require ‘foo\_constants’  
class Foo  
include FooConstants  
end

harp:~ \> cat bar.rb  
require ‘foo\_constants’  
class Bar  
include FooConstants  
def self.set\_foo(val)  
define\_method(:foo) { val }  
end  
end

harp:~ \> ruby foobar.rb  
42

hard to understand **why** you’d do that - but factoring module-wise  
will  
certainly lead to an elegant answer.

regards.

-a

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 15, 2006, 11:10pm UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558/5 "2006-05-15T23:10:52Z")

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On 5/15/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> 42
> 
> hard to understand **why** you’d do that - but factoring module-wise will  
> certainly lead to an elegant answer.

Thanks for the response Ara.

Do you mean it’s hard to understand why I’d set things up the way I  
have them? Or do you mean that factoring the constants out is a non  
obvious solution?

Anyway what really interests me is why I only have this problem when  
I’m calling the class method that calls define\_method inside it. If  
you look at it, instance methods and class methods all work fine. If  
it were purely a class loading issue, shouldn’t it blow up in other  
cases as well?

Pat

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<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 10:30am UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558/6 "2006-05-16T10:30:24Z")

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On 5/15/06, Austin Z. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> I think you’re going to need to be a bit clearer about what you’re  
> _actually_ trying to do, because this sounds like an incredibly bad  
> design.
> 
> Circular dependencies are bad.

I went through Ch1 of Refactoring, using rspec to write the tests.  
After I was done with all the refactorings, I wanted to be able to  
specify a price code for each Price class by calling a class method,  
rather than defining one. I’ve got all the source code at  
[http://svn.flpr.org/public/refactoringbdd](http://svn.flpr.org/public/refactoringbdd) It’s very small, so it  
wouldn’t take more than a few minutes to look at.

Here’s the original code for one class, with extraneous methods ripped  
out:

class ChildrensPrice \< Price  
def get\_price\_code  
Movie::CHILDRENS  
end  
end

Here’s what I’d like to do:  
class Price  
def self.price(val)  
define\_method(:get\_price\_code) { val }  
end  
end

class ChildrensPrice \< Price  
price Movie::CHILDRENS  
end

As you can see, instead of defining get\_price\_code, I just call  
Class.price and it defines the method for me.

Currently the test suite runs fine. If you open  
specs/customer\_spec.rb and delete the require “price” line though, it  
gives errors.

Pat

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**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 15, 2006, 11:17pm UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558/7 "2006-05-15T23:17:31Z")

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On 5/15/06, Pat M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > > end
> > 
> > to this:
> > 
> > # foo.rb
> > 
> > class Foo  
> > FOO = “foo”  
> > end  
> > require “bar”  
> > I can’t, because some of the methods in the Foo class call Bar methods.

Do you mean:

class Foo  
FOO = foo  
def initialize(mybar)  
@bar = mybar  
end

```
def baz
  # ... stuff ...
  @bar.baz
  # ... stuff ...
end

```

end

If that’s the case, then you can do it.

> > Better yet, get rid of your circular dependency.
> > 
> > FooBar should be defined in a third file that requires foo.rb and  
> > bar.rb.  
> > I’m not sure how that fixes anything. Foo has to create some Bar  
> > objects, and Bar has to have access to some of the Foo constants. I  
> > didn’t talk about that in my initial post, but each class interacts  
> > with each other.

I think you’re going to need to be a bit clearer about what you’re  
_actually_ trying to do, because this sounds like an incredibly bad  
design.

Circular dependencies are bad.

If you must absolutely have it, take advantage of Ruby’s open classes.  
But try to avoid it.

-austin

---

<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [May 16, 2006, 11:41am UTC](https://www.ruby-forum.com/t/weird-class-loading-issue-or-maybe-a-problem-with-define-me/60558/8 "2006-05-16T11:41:51Z")

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Pat M. schrieb:

> I’ve got all the source code at  
> [http://svn.flpr.org/public/refactoringbdd](http://svn.flpr.org/public/refactoringbdd) It’s very small, so it  
> wouldn’t take more than a few minutes to look at.

Pat, I haven’t looked very carefully, but noted two things:

Too many requires: for example, in customer.rb you require “rental”, but  
you don’t use the Rental class. Skip those require statements.

Duplicated knowledge: the connection between price codes and price  
subclasses is duplicated in Movie#price\_code= and in the price  
subclasses themselves. Try to remove this duplication. I don’t think it  
is a good idea that the Price class has to know something about price  
codes, which seems to be a concept of the Movie class.

Regards,  
Pit