# Defining a class without opening an existent one

**URL:** <https://www.ruby-forum.com/t/defining-a-class-without-opening-an-existent-one/195492>\
**Category:** Ruby\
**Created:** [September 23, 2010, 9:20pm UTC](https://www.ruby-forum.com/t/defining-a-class-without-opening-an-existent-one/195492 "2010-09-23T21:20:50Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![hagbard](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/d26b3c/32.png) [@hagbard](https://www.ruby-forum.com/u/hagbard)\
**Post date:** [September 23, 2010, 9:20pm UTC](https://www.ruby-forum.com/t/defining-a-class-without-opening-an-existent-one/195492/1 "2010-09-23T21:20:50Z")

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Hi there!

I want to define a class which happens to have the same name as a  
builtin class. It shouldn’t be a problem because it’s in an extra  
namespace, but Ruby opens the existing class instead of defining a new  
one. Here’s an example:

module MyNamespace  
class Array  
# Some stuff  
end  
end

I tried using the full qualifier (class MyNamespace::Array) but it  
didn’t help. Is there a possibility to actually define a new class?

---

<div class="post-metadata">

**Author:** ![hagbard](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/d26b3c/32.png) [@hagbard](https://www.ruby-forum.com/u/hagbard)\
**Post date:** [September 23, 2010, 9:50pm UTC](https://www.ruby-forum.com/t/defining-a-class-without-opening-an-existent-one/195492/2 "2010-09-23T21:50:21Z")

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Hagbard C. wrote:0

> I want to define a class which happens to have the same name as a  
> builtin class. It shouldn’t be a problem because it’s in an extra  
> namespace, but Ruby opens the existing class instead of defining a new  
> one. Here’s an example:
> 
> module MyNamespace  
> class Array  
> # Some stuff  
> end  
> end

That’s fine. What makes you think that this didn’t create a separate  
class?

> I tried using the full qualifier (class MyNamespace::Array) but it  
> didn’t help.

In what way didn’t it help? Did you get an error message? Post your full  
code and the exception.

> Is there a possibility to actually define a new class?

Sure, you’ve just done it 🙂

> > module MyNamespace; class Array; end; end  
> > =\> nil
> 
> > Array.object\_id  
> > =\> 70098182563360
> 
> > MyNamespace::Array.object\_id  
> > =\> 70098182326040
> 
> > a = MyNamespace::Array.new  
> > =\> #MyNamespace::Array:0x7f820281f520
> 
> > a[1]  
> > NoMethodError: undefined method `[]’ for  
> > #MyNamespace::Array:0x7f820281f520  
> > from (irb):5  
> > from :0

---

<div class="post-metadata">

**Author:** ![hagbard](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/d26b3c/32.png) [@hagbard](https://www.ruby-forum.com/u/hagbard)\
**Post date:** [September 23, 2010, 9:59pm UTC](https://www.ruby-forum.com/t/defining-a-class-without-opening-an-existent-one/195492/3 "2010-09-23T21:59:17Z")

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All of a sudden, the scales fall from my eyes. At first I wasn’t so sure  
whether I defined a new class or not myself. I looked at the methods of  
the class and something made me think that they were the same as  
`Array`s. Retrospectively, I don’t know what made me think so. Thanks  
for your help.

---

<div class="post-metadata">

**Author:** ![hagbard](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/d26b3c/32.png) [@hagbard](https://www.ruby-forum.com/u/hagbard)\
**Post date:** [September 25, 2010, 5:10pm UTC](https://www.ruby-forum.com/t/defining-a-class-without-opening-an-existent-one/195492/4 "2010-09-25T17:10:21Z")

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Robert K. wrote:

> creation of a class with the same name as one of  
> the core classes does not seem like a good idea to me - although it’s  
> certainly possible. It may cause confusion and it also makes using  
> the core class more cumbersome (you need to reference it as ::Array in  
> the module and nested classes for example).

That’s true but unfortunately `Array` is just the perfect name for my  
class. I rather use MyNamespace::Array and ::Array instead of inventing  
a bad-fitting name for the class.

---

<div class="post-metadata">

**Author:** ![hagbard](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/d26b3c/32.png) [@hagbard](https://www.ruby-forum.com/u/hagbard)\
**Post date:** [September 24, 2010, 12:42pm UTC](https://www.ruby-forum.com/t/defining-a-class-without-opening-an-existent-one/195492/5 "2010-09-24T12:42:36Z")

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On Thu, Sep 23, 2010 at 9:59 PM, Hagbard C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> All of a sudden, the scales fall from my eyes. At first I wasn’t so sure  
> whether I defined a new class or not myself. I looked at the methods of  
> the class and something made me think that they were the same as  
> `Array`s. Retrospectively, I don’t know what made me think so. Thanks  
> for your help.

Just adding 0.02EUR: creation of a class with the same name as one of  
the core classes does not seem like a good idea to me - although it’s  
certainly possible. It may cause confusion and it also makes using  
the core class more cumbersome (you need to reference it as ::Array in  
the module and nested classes for example).

Kind regards

robert