From: "David A. Black" <dblack@...>
Date: 2005-07-23T10:46:11+09:00
Subject: Re: FAQ? Hash concatenation

Hi --

On Sat, 23 Jul 2005, William James wrote:

>
>
> Mark J. Reed wrote:
>> I've read matz's explanation for the lack of a concatenation operator for
>> Hashes in Ruby, but I was wondering if there were a module that supplied one
>> anyway.  Or at least a self-modifying method that works like update() but
>> without clobbering existing values.
>
> h={'a',1, 'c',3, 'd',4}
> h={'a',99, 'b',2}.update(h)
>  -->  {"a"=>1, "b"=>2, "c"=>3, "d"=>4}

However....

irb(main):006:0> h={'a',1, 'c',3, 'd',4}
=> {"a"=>1, "c"=>3, "d"=>4}
irb(main):007:0> h.object_id
=> 537888058
irb(main):008:0>  h={'a',99, 'b',2}.update(h)
=> {"a"=>1, "b"=>2, "c"=>3, "d"=>4}
irb(main):009:0> h.object_id
=> 537863828

So if it matters that it be the same object, this technique won't be
appropriate.  Also, if you're using something other than a hash
literal, for example:

   h1 = h2.update(h1)

you're going to change h2, which might also be undesireable in some
cases.


David

-- 
David A. Black
dblack@wobblini.net