From: Eric Hodel <drbrain@...7.net>
Date: 2007-01-10T06:15:56+09:00
Subject: Re: String performance

On Jan 9, 2007, at 12:53, Vincent Fourmond wrote:
> George Palmer wrote:
>> Guys a quick performance question - Is either one of the following  
>> more
>> efficient than the other?  I'm guessing they're in this order:
>>
>> 'a' + x + 'b'
>> "a" + x + "b"
>> "a#{x}b"
>
>   Exactly the opposite:
>
>
> 21:52 vincent@tanyaivinco ~/Prog/Ruby ruby rt_7.rb
>       user     system      total        real
>   0.010000   0.000000   0.010000 (  0.009087)
>   0.010000   0.000000   0.010000 (  0.008774)
>   0.000000   0.000000   0.000000 (  0.004621)
>
> rt_7.rb is

Could be improved:

$ cat rt_7.rb
require 'benchmark'

n = 5_000_000
c = "stuff"
Benchmark.bmbm do |x|
   x.report('\'a\' +') { n.times {'a' + c + 'b'}}
   x.report('"a" +') { n.times {"a" + c + "b"}}
   x.report('a#{') { n.times {"a#{c}b"}}
end

$ ruby rt_7.rb
Rehearsal -----------------------------------------
'a' +   6.090000   0.010000   6.100000 (  6.183097)
"a" +   6.110000   0.010000   6.120000 (  6.114159)
a#{     3.280000   0.000000   3.280000 (  3.298253)
------------------------------- total: 15.500000sec

             user     system      total        real
'a' +   6.130000   0.010000   6.140000 (  6.155325)
"a" +   6.140000   0.000000   6.140000 (  6.155082)
a#{     3.300000   0.010000   3.310000 (  3.312989)

Further increases in n will show ' strings and " strings completely  
converging.  To the interpreter there is no difference between the two:

$ parse_tree_show -f
'a' + stuff + 'b'
"a" + stuff + "b"
"a#{stuff}b"
(eval):1: warning: useless use of + in void context
(eval):2: warning: useless use of + in void context
[[:call,
   [:call, [:str, "a"], :+, [:array, [:vcall, :stuff]]],
   :+,
   [:array, [:str, "b"]]],
  [:call,
   [:call, [:str, "a"], :+, [:array, [:vcall, :stuff]]],
   :+,
   [:array, [:str, "b"]]],
  [:dstr, "a", [:vcall, :stuff], [:str, "b"]]]

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net

I LIT YOUR GEM ON FIRE!