From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2012-01-14T23:56:30+09:00
Subject: Re: Language deisng question and stinrgs and object id's

On Sat, Jan 14, 2012 at 3:38 PM, Ralph Shnelvar <ralphs@dos32.com> wrote:
>  a = "string"
>  b = "string"
>
>  causes three objects with different object id's to be created.

It actually causes just two objects to be created.

>
>  irb(main):001:0>  a = "string"
> => "string"
> irb(main):002:0>  b = "string"
> => "string"
> irb(main):003:0> "string".object_id
> => 19087248

This one is a new and different thing that is not related to your
above two lines of code at all.

> irb(main):004:0> a.object_id
> => 21660552
> irb(main):005:0> b.object_id
> => 22419972
>

I think what you are missing is that a literal String creates a new
string object. The fact that the characters are the same doesn't mean
it's the same object:

1.9.2p290 :001 > "string".object_id
 => 14124100
1.9.2p290 :002 > "string".object_id
 => 14101660
1.9.2p290 :003 > "string".object_id
 => 14081660
1.9.2p290 :004 > "string".object_id
 => 14068260

> Yet
>  a = "string"
>  b = a
> only causes two objects to be created.

It actually only causes one object to be created, see above.

> irb(main):001:0>   a = "string"
> => "string"
> irb(main):002:0>   b = a
> => "string"
> irb(main):003:0> "string".object_id
> => 22106544
> irb(main):004:0> a.object_id
> => 22650984
> irb(main):005:0> b.object_id
> => 22650984

A possible misunderstanding here would be to miss the difference
between an object and a variable. A variable is a reference to an
object. Several variables can reference the same object. Assigning
variables only changes what they reference, not the objects
themselves.

> Yes, I know that one can do
>
>  a = "string"
>  b = a.clone
>
> I understand what's happening.  I just don't know why the language designer(s) decided on -- what is to me -- surprising behavior.

I think that having objects be a separate concept from the variables
that reference them is pretty common, and provides very nice language
semantics.
Just think that a literal string is a new object every time it
appears, the same with hashes, for example.

> So I have a Car Talk Puzzler (for which I do not have an answer): How would I initialize a bunch of strings so that they are clones rather than the same object?
>
> In other words how would I do the following which is invalid Ruby.
>
> a = b.clone = c.clone = "How to clone?"

1.9.2p290 :005 > a = (b = (c = "How to clone?").clone).clone
 => "How to clone?"
1.9.2p290 :006 > [a.object_id, b.object_id, c.object_id]
 => [14045460, 14045480, 14045520]
1.9.2p290 :007 > [a,b,c]
 => ["How to clone?", "How to clone?", "How to clone?"]

Jesus.