From: Gennady Bystritsky <Gennady.Bystritsky@...>
Date: 2010-04-02T17:09:42+09:00
Subject: Re: scope question


On Apr 2, 2010, at 12:39 AM, Harry Kakueki wrote:

> Maybe I'm missing something obvious here, but...

I am afraid, you are. Hopefully not for long ;-)

> Does this result surprise anyone else or just me?
> I was expecting a_hash and an_arr to be local to the method.
> Did I just do something stupid?
> 
> 
> def scope_q(a_hash,an_arr,a_num)

a_hash, an_arr and a_num are local to the method indeed. However, a_hash and an_array hold references to hash and array object respectively, not copies. So you are changing the objects passed to this method via those references. On the other hand, a_num is passed a Fixnum instance which are implemented as immediate objects and hence passed as copy.

>  a_hash["b"] = 3
>  an_arr[1] = 5
>  a_num += 1
> end
> 
> h = {"a"=>1,"b"=>2,"c"=>3,"d"=>4}
> a = [1,2,3,4]
> n = 7
> 
> scope_q(h,a,n)

Here where you pass references to Hash h and Array a, and n as an immediate object 7.

> 
> p h  #> {"a"=>1, "b"=>3, "c"=>3, "d"=>4}

Changed in the method

> p a  #> [1, 5, 3, 4]

Changed in the method

> p n  #> 7

Not changed as the methods incremented a copy.

> 
> 
> #ruby 1.9.1p243

All ruby versions work identically in this area.

> 
> 
> Harry
>