From: Kent Dahl <kentda@...>
Date: 2002-10-17T17:46:33+09:00
Subject: Re: Strings or symbols?

Gavin Sinclair wrote:
> Given all this, I would use Strings if I were you.  For plain indices that
> don't really need to be interpreted outside the hash, I use symbols.  I think
> symbols are more efficient, too (but probably not if you're converting them to
> strings all the time).

Or converting strings to symbols, if I understood the OP correctly :-)

As I understand it, the potential gain in using symbols, is depending on
how the hash value is computed. Since a symbol is an internalized
string, it could potentially be quicker. I tried a quick and dirty
profiling test. Not surprising, using symbols are quicker than using
strings. Naturally stringifying a symbol or interning a string before
hash lookup is slower than either of the above. (Quite surprising to me,
they both appear to be approximately equal in time usage.)

So it is a matter of weighing how many times you guess you will be
looking up with symbols directly versus when you need to internalize a
string. If the script sets the variables from the CGI once (requiring an
intern to get symbol), but access it in the script elsewhere using
symbol a lot of times, symbols would be the way to go. (CGI
communication usually is slow as heck anyway, since you probably have a
user infront of a HTML form being the slowest link :-)


<CODE file="symbol.rb">
require 'profile'

N = 10000
H = { :abba => ':A', 'abba' => 'A' }

def time_strings
  N.times do |i| H['abba'] end
end 
def time_string_interned
  N.times do |i| H['abba'.intern] end
end 
def time_symbols
  N.times do |i| H[:abba] end
end 
def time_symbols_stringified
  N.times do |i| H[:abba.to_s] end
end 

time_strings
time_symbols
time_string_interned
time_symbols_stringified
</CODE>

<OUTPUT>
[kentda@v052a ruby]$ /usr/local/bin/ruby symbol.rb          
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 63.43     7.13      7.13        4  1782.50  2810.00  Integer#times
 14.41     8.75      1.62    40000     0.04     0.04  Hash#[]
  9.07     9.77      1.02    30004     0.03     0.03  String#allocate
  8.99    10.78      1.01    10000     0.10     0.13  Symbol#to_s
  4.09    11.24      0.46    10000     0.05     0.05  String#intern
  0.00    11.24      0.00        1     0.00 11240.00  #toplevel
  0.00    11.24      0.00        1     0.00  1390.00 
Object#time_symbols
  0.00    11.24      0.00        1     0.00  3680.00 
Object#time_symbols_stringified
  0.00    11.24      0.00        4     0.00     0.00 
Module#method_added
  0.00    11.24      0.00        1     0.00  2520.00 
Object#time_strings
  0.00    11.24      0.00        1     0.00  3650.00 
Object#time_string_interned
[kentda@v052a ruby]$ /usr/local/bin/ruby --version           
ruby 1.7.2 (2002-07-13) [i686-linux]
</OUTPUT>

-- 
(\[ Kent Dahl ]/)_    _~_    __[ http://www.stud.ntnu.no/~kentda/ ]___/~
 ))\_student_/((  \__d L b__/  NTNU - graduate engineering - 5. year  )
( \__\_�|�_/__/ ) _)Industrial economics and technological management(
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