From: Rick DeNatale <rick.denatale@...>
Date: 2009-04-02T16:48:53+09:00
Subject: Re: Symbols garbage collector in Ruby1.9, fixed?

--001636163c5f4de98104668dabc0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

On Thu, Apr 2, 2009 at 12:17 AM, Rob Biedenharn
<Rob@agileconsultingllc.com>wrote:

>
> If you really need to use symbols, perhaps add methods to a subclass of
> Hash like the HashWithIndifferentAccess from Rails which mostly eliminates
> the need to care whether you actually stored against a Symbol or a String
> key.
>
> There's also nothing stopping you from having both kinds of keys at once:
>  headers = { :from => "alice@qweeq", :to => "bob@qweeq", 'snack' =>
> "raisins" }
>
> but then you might have to "worry" about having both :to and 'to' as keys.
>
> Symbols are only faster because they are immutable and don't get garbage
> collected. But I'd go with Tony and just use String all the time.
>

Actually, I'm pretty sure that Symbols are faster as hash keys because
Hash#== is O(1) while String#== is O(n) where n is the length of the string.
That said, the HashWithIndifferentAccess class in activesupport  allows
either strings or symbols to be used interchangeably as the key argument in
methods like [] and []=, but it always USES the string form as the key.

I was quite surprised when I discovered this, since I'd assumed that the
reason for using symbols was for the speed advantage, but it was finally
pointed out to me the problem of "memory leaks" when arbitrary keys get
interned as symbols.

But I do in general prefer the look in source code of

   :id => 3

rather than

   'id' = > 3

And when the symbols come in the source like this there's less chance of
arbitrary growth of interned symbols.

-- 
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale

--001636163c5f4de98104668dabc0--