From: Lionel Thiry <lthiryidontwantspams@...>
Date: 2005-12-01T20:37:31+09:00
Subject: Re: Point an element in Hash Object

Ross Bamford a 辿crit :
> On Wed, 30 Nov 2005 22:05:53 -0000, Andrew <andrea.reginato@gmail.com> 
> wrote:
> 
>> I'm trying to create an hash object using object string for key and
>> value.
>> I need to link a key with another key as value... so an element of hash
>> object can  point to another element. But i need the link to the key and
>> not a copy of the value.
>>
>> I have tried in this way:
>> @my_hash["one"] = "First"
>> @my_hash["two"] = "Second"
>> @my_hash["three"] = "Third"
>> @my_hash["four"] = @my_hash["T1"]
>>
>> Now if I modify
>> @my_hash["one"] = "Modify"
>> I would like to see the new value also for
>> @my_hash["four"]  =>  "Modify"
>> but I see "First" because i think it do a copy.
>>
>> The problem is that i woult like to refer the element end not to copy
>> it.
>> Thanks so much and sorry for my english.
>>
>> Andreaw
>>
> 
> (Caveat: Fairly new to Ruby)
> 
> You actually do have a reference - AFAIU so far, pretty much everything
> is  passed by reference (except references, which are passed by value
> ;)).  Prior to your '@my_hash["one"] = "Modify"' they do both reference
> the same  object, but then you replace the reference with a new
> reference, to a  string "Modify".
> 
> Swap
> 
>     @my_hash["one"] = "Modify"
> 
> for
> 
>     @my_hash["one"].sub!(/First/,'Modify')

@my_hash["one"].replace 'Modify'
is better

> 
> and you should get the result you want, because 'sub!' modifies the 
> receiver, so no new reference is assigned to @my_hash["one"].
> 
> (N.B. that this just illustrates the problem more, it's not a general 
> solution. For that I'd probably use a holder for the string (maybe an 
> one-element array), but I don't fully know what Ruby has to offer
> instead  yet ;)
> 


-- 
Lionel Thiry

Personal web site: http://users.skynet.be/lthiry/