# Ruby Q's

**URL:** <https://www.ruby-forum.com/t/ruby-qs/140504>\
**Category:** Ruby\
**Created:** [June 15, 2008, 11:06am UTC](https://www.ruby-forum.com/t/ruby-qs/140504 "2008-06-15T11:06:50Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [June 15, 2008, 11:06am UTC](https://www.ruby-forum.com/t/ruby-qs/140504/1 "2008-06-15T11:06:50Z")

</div>

Hi I’ve been doing rails for a while, which was really my first  
introduction to ruby. I’ve found my self using ruby more and more and  
keep amazing my self about how cool it is, although I’ve got a few  
questions, or rather holes in my ruby knowledge, from rails doing a lot  
of stuff for you I think.

1. What does a double colon do in terms of class inheritance. ie.  
GameWindow \< Gosu::Window ?

2. Why would you want to use nested classes?

3. Is it bad practice to define constance out of classes?

4. How/Can you delete instance variables or objects?

---

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [June 15, 2008, 11:24am UTC](https://www.ruby-forum.com/t/ruby-qs/140504/2 "2008-06-15T11:24:41Z")

</div>

Phil Cooper-king wrote:

> 1. What does a double colon do in terms of class inheritance.

Nothing.

> ie. GameWindow \< Gosu::Window ?

This means that GameWindow inherits from the class Gosu::Window, which  
is the  
class Window in the namespace Gosu.

> 1. Why would you want to use nested classes?

To avoid name collision or just to group things together that belong  
together  
or keep classes that won’t be directly used by the user out of the main  
namespace. Like if you have a class Card that uses the class Rank, but  
the  
user won’t ever create an instance of class Rank himself (he just will  
get  
Rank object when he does my\_card.rank), you’d nest Rank inside Card (and  
Card  
probably inside MyGame, for the previous reasons).

> 1. Is it bad practice to define constance out of classes?

Not as such, but it’s generally a good idea - at least for libraries  
that will  
be used by other ruby files, to have all your stuff in a namespace to  
avoid  
name collision as in point 2.

> 1. How/Can you delete instance variables

Just set them to nil or use remove\_instance\_variable (the former won’t  
actually delete the variable, but why do you need to do that anyway?)

> or objects?

An objects gets GCed when it’s no longer referenced by any variables.

HTH,  
Sebastian

---

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [June 15, 2008, 11:34am UTC](https://www.ruby-forum.com/t/ruby-qs/140504/3 "2008-06-15T11:34:04Z")

</div>

On Sunday 15 June 2008, Phil Cooper-king wrote:

> Hi I’ve been doing rails for a while, which was really my first  
> introduction to ruby. I’ve found my self using ruby more and more and  
> keep amazing my self about how cool it is, although I’ve got a few  
> questions, or rather holes in my ruby knowledge, from rails doing a lot  
> of stuff for you I think.
> 
> 1. What does a double colon do in terms of class inheritance. ie.  
> GameWindow \< Gosu::Window ?

Nothing special. As always, it’s used to access a constant defined in  
another  
class or module. In your specific example, it is used to access the  
Window  
class in the Gosu module so that the GameWindow class can inherit it. It  
is  
exactly the same as:

window = Gosu::Window

class GameWindow \< window

> 1. Why would you want to use nested classes?  
> Personally, I use nested classes when the inner class is closey coupled  
> to the  
> outer and isn’t meant to be used by itself(for example, it can be a  
> helper  
> class used by the implementation of the outer class and which isn’t  
> useful if  
> used in other ways). They don’t provide additional benefits, but make  
> clearer  
> the programmer’s intent

> 1. Is it bad practice to define constance out of classes?  
> Constants defined outside classes are top level constants, so the answer  
> depends on the meaning of the constant. If it is related to the  
> application or  
> library as a whole, it may make sense to define it globally (for  
> example, a  
> constant containing the application version). If it is specific of a  
> class,  
> put it there (for example, take the constants defined in class Regexp.  
> They  
> are meant to be used only in methods of that class, so it wouldn’t make  
> sense  
> to define it globally).

> 1. How/Can you delete instance variables or objects?  
> It depends on what you exactly mean, but I’d say the answer is no. I  
> don’t  
> think you can force an object to be garbage-collected, and you cant  
> undefine  
> an instance variable. What you can do is to make possible for the object  
> to be  
> garbage-collected by setting all variables which point to it to  
> something else  
> and set an instance variable to nil.

Stefano

---

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [June 15, 2008, 11:39am UTC](https://www.ruby-forum.com/t/ruby-qs/140504/4 "2008-06-15T11:39:57Z")

</div>

On Sunday 15 June 2008, Stefano C. wrote:

> and you cant undefine an instance variable.
> 
> Stefano

Sorry, I misread the documentation. You can indeed undefine an instance  
variable, using the remove\_instance\_variable method. Since it is  
private,  
though, if you need to call it from outside the instance, you can either  
use  
send

obj.send :remove\_instance\_variable :@var

or make the method public

class C

public :remove\_instance\_variable  
end

Stefano

---

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [June 15, 2008, 11:25am UTC](https://www.ruby-forum.com/t/ruby-qs/140504/5 "2008-06-15T11:25:52Z")

</div>

> 1. What does a double colon do in terms of class inheritance. ie.  
> GameWindow \< Gosu::Window ?

Nothing. It’s a namespace thing.

> 1. Why would you want to use nested classes?

In order not to pollute the global namespace.

> 1. Is it bad practice to define constance out of classes?

It depends on whether you care about polluting the global namespace.  
IMHO, yes.

> 1. How/Can you delete instance variables or objects?

By removing references to it (unsetting variables pointing to the  
object) and letting the garbage collector do its work. I’m not sure  
what you mean with “delete instance variables”.

I hope the answers are about right. If not, please somebody correct  
me.

---

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [June 15, 2008, 6:54pm UTC](https://www.ruby-forum.com/t/ruby-qs/140504/6 "2008-06-15T18:54:26Z")

</div>

Phil Cooper-king wrote:

> Thanks guys.
> 
> the Gosu::Window thing would that be an example of nested then? as in  
> Gosu module Window class?

Yes.

> the deleting instance var object was something that I was trying to do  
> in regards to Gosu Game lib.  
> it tries to update itself 60 times a second, so if you press a key it  
> gets regstered by the lib several times. I was trying to create a method  
> that it would once the key was pressed it remained inactive for a set  
> time. I was using the Gosu::milliseconds for this. it seemed easier to  
> create a class that handled this, and I was getting worried that it  
> would create loads of objects that only had a short life span then  
> sucked up perfomance as the game continued. but if they delete them self  
> if there is no pointer to them that works.

In your key handling method, wrap the logic in something like  
if not @pause\_end or Gosu::milliseconds \> @pause\_end

# …

end

After you handle whatever key was pressed, just add a line like:

@pause\_end = Gosu::milliseconds + 500 # or however long you want it to  
be inactive

---

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [November 3, 2008, 4:12am UTC](https://www.ruby-forum.com/t/ruby-qs/140504/7 "2008-11-03T04:12:49Z")

</div>

In regards to this post, a more relevant example of an instance variable  
reference problem is the following:

In a Game Object, there is an Area object.  
An area object has Player A and Player B, which are themselves objects.

When Player A interacts (such as attacks) Player B, both objects store a  
reference to each other in order to interact.

So in this sense, the Game Object, Area Object and both players have  
reference to player objects.

Now, if Player A quits the game, the Game Object might make the  
reference to the Player A = nil.

It would be very helpful to be able to destroy the object, without  
having to find all objects referencing this object to finally get Player  
A to become nil.

I would appreciate help on this matter, on how to make a single object  
nil and have that propagate to everything referencing it.

---

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [June 15, 2008, 11:42am UTC](https://www.ruby-forum.com/t/ruby-qs/140504/8 "2008-06-15T11:42:07Z")

</div>

Thanks guys.

the Gosu::Window thing would that be an example of nested then? as in  
Gosu module Window class?

the deleting instance var object was something that I was trying to do  
in regards to Gosu Game lib.  
it tries to update itself 60 times a second, so if you press a key it  
gets regstered by the lib several times. I was trying to create a method  
that it would once the key was pressed it remained inactive for a set  
time. I was using the Gosu::milliseconds for this. it seemed easier to  
create a class that handled this, and I was getting worried that it  
would create loads of objects that only had a short life span then  
sucked up perfomance as the game continued. but if they delete them self  
if there is no pointer to them that works.

---

<div class="post-metadata">

**Author:** ![basic](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/58956e/32.png) [@basic](https://www.ruby-forum.com/u/basic)\
**Post date:** [November 3, 2008, 1:49pm UTC](https://www.ruby-forum.com/t/ruby-qs/140504/9 "2008-11-03T13:49:17Z")

</div>

Andres Colon wrote:

> reference to player objects.
> 
> Now, if Player A quits the game, the Game Object might make the  
> reference to the Player A = nil.
> 
> It would be very helpful to be able to destroy the object, without  
> having to find all objects referencing this object to finally get Player  
> A to become nil.
> 
> I would appreciate help on this matter, on how to make a single object  
> nil and have that propagate to everything referencing it.

Two approaches come to mind. The first is make the Game Object  
observable (see observable.rb). When it is destroyed it notifies the  
objects that refer to it.

The second is to pass around an indirect reference to the Game Object.  
For example, make an array that contains only the Game Objecct and give  
the players a reference to the array. When the Game Object is destroyed  
it sets the array element to nil. The players never refer to the game  
object directly, only via the array and only after making sure it hasn’t  
become nil.