From: Robert Klemme <shortcutter@...>
Date: 2011-01-13T21:15:24+09:00
Subject: Re: Why {} is much faster than Hash.new ?

On Thu, Jan 13, 2011 at 12:05 PM, Iņaki Baz Castillo <ibc@aliax.net> wrote:
> Hi, a simple benchmark:
>
> Benchmark.realtime { 1000000.times { @m = Hash.new } }
> => 0.6552023887634277
>
> Benchmark.realtime { 1000000.times { @m = {} } }
> => 0.17668819427490234
>
> I would like to know why {} is so much faster. I can understand that
> Hash.initialize method must inspect is an argument is given and so, is
> just due to it?

I can imagine that's about right.  Another benchmark:

13:10:40 Temp$ ruby19 bm.rb
Rehearsal --------------------------------------------------
Hash.new         1.297000   0.000000   1.297000 (  1.293000)
Hash             0.125000   0.000000   0.125000 (  0.127000)
Hash.nil?        0.187000   0.000000   0.187000 (  0.186000)
{}               0.188000   0.000000   0.188000 (  0.191000)
----------------------------------------- total: 1.797000sec

                     user     system      total        real
Hash.new         1.296000   0.000000   1.296000 (  1.292000)
Hash             0.125000   0.000000   0.125000 (  0.127000)
Hash.nil?        0.188000   0.000000   0.188000 (  0.185000)
{}               0.187000   0.000000   0.187000 (  0.191000)
13:10:50 Temp$ cat bm.rb
require 'benchmark'

R = 1_000_000

Benchmark.bmbm 15 do |b|
  b.report "Hash.new" do
    R.times { Hash.new }
  end

  b.report "Hash" do
    R.times { Hash }
  end

  b.report "Hash.nil?" do
    R.times { Hash.nil? }
  end

  b.report "{}" do
    R.times { {} }
  end
end
13:10:52 Temp$

Cheers

robert

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