From: Mathieu Bouchard <matju@...>
Date: 2001-06-22T15:52:28+09:00
Subject: [ruby-talk:16750] Re: Symbols, and their use as hash keys

On Fri, 22 Jun 2001, Aristarkh A Zagorodnikov wrote:
> 	May anyone enlighten me with knowledge of how symbol integer value
> (Symbol#to_i) is generated ?

It's the integer that would be returned if you were running Ruby 1.4
instead (which had a symbol table, but no Symbol objects)

> Also, I'm interested why using it as a hash key is about 5-8 times
> slower then string of the same size ?

 time     expr
 0.07 s   100000.times{}
 0.53 s   100000.times{{}}
 1.09 s   100000.times{{1  =>1,2  =>2,3  =>3}}
 1.09 s   100000.times{{:x =>1,:y =>2,:z =>3}}
 1.68 s   100000.times{{"x"=>1,"y"=>2,"z"=>3}}

This test indicates that, for small strings, symbol and integer keys are
twice faster than 1-char strings.

(note: if you preassign to local variables in the last test, it drops to
1.50 s)

I get similar results by assigning to a pre-existing hash.

> 	I understand that Symbols are not intended for this purpose,

They are intended for small numbers of small strings that are used often.
They can be fast in a hash.

However if you use lots and lots of symbols, it may be slower. (note that
symbols are *never* garbage-collected, so don't abuse them)

matju