From: Brian Mitchell <binary42@...>
Date: 2006-04-13T03:55:02+09:00
Subject: Re: First script seems slow - What's a better way to write t

2006/4/12, Logan Capaldo <logancapaldo@gmail.com>:
> You use this idiom:
>
> class SomeClass
>    def initialize
>      @some_re = /some_re/
>    end
>    def some_method
>       # do stuff with @some_re
>    end
> end

Actually, Ruby is quite smart in some cases.. Try the following:

@re = /^\w+-\w+$/ # Some random expression
def foo(str)
  str =~ @re
end

def bar(str)
  str =~ /^\w+-\w+$/
end

def qux(str)
 str =~ Regexp.new("/^\w+-\w+$/")
end

require 'benchmark'
include Benchmark

bm(16) do |test|
  test.report("foo") do
    1_000_000.times {foo("abc-xyz")}
  end
  test.report("bar") do
    1_000_000.times {bar("abc-xyz")}
  end
  test.report("qux") do
    1_000_000.times {qux("abc-xyz")}
  end
end

I get something like this on 1.8 cvs:

                      user     system      total        real
foo               4.920000   0.080000   5.000000 (  5.581873)
bar               4.610000   0.060000   4.670000 (  5.457461)
qux              15.280000   0.280000  15.560000 ( 17.514639)

So ruby actually shares a single compiled Regexp object in bar's case
(as can also be proven by counting Regexp's in ObjectSpace with the GC
disabled).

Brian.