From: Joel VanderWerf <vjoel@...>
Date: 2007-09-07T00:05:05+09:00
Subject: Re: Symbols and frozen strings

Brian Candler wrote:
> I just had a thought.
> 
> One of the problems with using strings as hash keys is that every time you
> refer to them, you create a throw-away garbage string:
> 
>     params["id"]
>             ^
>             +-- temporary string, needs to be garbage collected

Setting aside the question of freezing, why can't ruby share string data 
for all strings generated from the same symbol? And in that case you 
could do the following to avoid garbage:

      params[:id.to_s]

(Or ruby could even look up the literal "id" in the symbol table and do 
this for you.)

This code shows some of the cases in which ruby does and does not share 
string contents:


def show_vmsize
   GC.start
   puts `ps -o vsz #$$`[/\d+/]
end

s = "a"*1000
sym = s.to_sym

show_vmsize # 8712

# ruby apparently does not share storage for strings derived
# from the same symbol:

strs1 = (0..10_000).map do
   sym.to_s
end

show_vmsize # 18488

# ruby does share storage for string ops:

strs2 = (0..10_000).map do
   s[0..-1]
end

show_vmsize # 18616

strs3 = (0..10_000).map do
   s.dup
end

show_vmsize # 18616

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407