# Anobject question

**URL:** <https://www.ruby-forum.com/t/anobject-question/61409>\
**Category:** Ruby\
**Created:** [May 23, 2006, 10:13pm UTC](https://www.ruby-forum.com/t/anobject-question/61409 "2006-05-23T22:13:54Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![narizona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/5daacb/32.png) [@narizona](https://www.ruby-forum.com/u/narizona)\
**Post date:** [May 23, 2006, 10:13pm UTC](https://www.ruby-forum.com/t/anobject-question/61409/1 "2006-05-23T22:13:54Z")

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In prag ruby the purchased copy, the following code fragment is shown.  
Look at where I added the \>\>\>\>. That line VU.new(@volume.succ). What I  
think it should do is create a new object instance of the class. What  
it does though is it increments the attribute @volume on an existing  
object that uses the succ method.

I have verified that it does not create a new object by using  
myObject.object\_id. I am sure this is basic oop stuff but I do not  
think I have seen it. Why does this happen like this?

I would have used an accessor to set the @volume. I am surprised by the  
use of new here.

Thanks for your insight.

\_Nathan

class VU  
include Comparable  
attr :volume  
def initialize(volume) # 0…9  
@volume = volume  
end  
def inspect  
‘#’ \* @volume  
end

# Support for ranges

def \<=\>(other)  
self.volume \<=\> other.volume  
end  
def succ  
raise(IndexError, “Volume too big”) if @volume \>= 9

> > > > VU.new(@volume.succ) \<\<\<\<\<  
> > > > end  
> > > > end

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**Author:** ![narizona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/5daacb/32.png) [@narizona](https://www.ruby-forum.com/u/narizona)\
**Post date:** [May 23, 2006, 10:30pm UTC](https://www.ruby-forum.com/t/anobject-question/61409/2 "2006-05-23T22:30:52Z")

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narizona wrote:

> In prag ruby the purchased copy, the following code fragment is shown.  
> Look at where I added the \>\>\>\>. That line VU.new(@volume.succ). What I  
> think it should do is create a new object instance of the class. What  
> it does though is it increments the attribute @volume on an existing  
> object that uses the succ method.
> 
> I have verified that it does not create a new object by using  
> myObject.object\_id.

Try running the code like this …

v = VU.new(0)  
v2 = v.succ

p v.volume, v.object\_id  
p v2.volume, v2.object\_id

Does that do what you expect?

– Jim W.

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**Author:** ![narizona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/5daacb/32.png) [@narizona](https://www.ruby-forum.com/u/narizona)\
**Post date:** [May 23, 2006, 10:45pm UTC](https://www.ruby-forum.com/t/anobject-question/61409/3 "2006-05-23T22:45:49Z")

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> def \<=\>(other)  
> self.volume \<=\> other.volume  
> end  
> def succ  
> raise(IndexError, “Volume too big”) if @volume \>= 9
> 
> > > > > VU.new(@volume.succ) \<\<\<\<\<  
> > > > > end  
> > > > > end

Typically, methods like `succ` don’t change the state of an object,  
but instead return a new object. Example:

i=1  
i.succ # returns 2, but the return value is discarded…  
i # i=\>1 , i is still 1  
x=i.succ  
i # i=\>1, i is STILL 1  
x # x=\>2 , method returned 2

Another example, if you sort an Array using `sort`, a new, sorted  
array is returned and the original array is left unsorted.

arr = [5,4,3,2,1]  
arr\_sorted = arr.sort  
arr\_sorted # [1,2,3,4,5]  
arr # [5,4,3,2,1] still unsorted

Methods that behave like this often have a counterpart that does it’s  
work in place. Those method’s names end with an exclamation point:  
`sort!`

arr = [5,4,3,2,1]  
arr.sort!  
arr # [1,2,3,4,5]

So for the above example, you have 2 options:

vu = VU.new(1)  
vu = vu.succ

or, implement an `succ!` method, that changes the volume in place.

…  
def succ!  
raise(IndexError, “Volume too big”) if @volume \>= 9  
@volume+=1  
end  
…

Then you can just call `vu.succ!`

-tim

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<div class="post-metadata">

**Author:** ![narizona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/5daacb/32.png) [@narizona](https://www.ruby-forum.com/u/narizona)\
**Post date:** [May 23, 2006, 10:58pm UTC](https://www.ruby-forum.com/t/anobject-question/61409/4 "2006-05-23T22:58:16Z")

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Very nice! Thank you very much. That helps.

Tim B. wrote: