bench.rb

require 'benchmark'

class Hash
  def orig_symbolize_keys!
    keys.each do |key|
      self[(key.to_sym rescue key) || key] = delete(key)
    end
    self
  end

  def symbolize_keys!
    keys.each do |key|
      self[(key.to_sym rescue key)] = delete(key) if key.respond_to?(:to_sym) && !key.is_a?(Fixnum)
    end
    self
  end
end

HASH1 = { 'a' => :a, nil => nil, :b => :b, 1 => 1, [] => [] }

HASH2 = { 'a' => :a, :b => :b, 1 => 1, [] => [] }

STR_HASH = { 'string1' => 'a', 'string2' => 'b', 'string3' => 'c', 'string4' => 'd' }

TESTS = 100_000
Benchmark.bmbm do |results|
  results.report("Hash#orig_symbolize_keys! , nil key") { TESTS.times { HASH1.orig_symbolize_keys! } }
  results.report("Hash#symbolize_keys! , nil key") { TESTS.times { HASH1.symbolize_keys! } } 
  results.report("Hash#orig_symbolize_keys!") { TESTS.times { HASH2.orig_symbolize_keys! } }
  results.report("Hash#symbolize_keys!") { TESTS.times { HASH2.symbolize_keys! } } 
  results.report("Hash#orig_symbolize_keys!, string keys") { TESTS.times { STR_HASH.orig_symbolize_keys! } }
  results.report("Hash#symbolize_keys!, string keys") { TESTS.times { STR_HASH.symbolize_keys! } } 
end

gistfile2.txt

methodmissing:~ lourens$ ruby hash_bench.rb
Rehearsal -----------------------------------------------------------------------
Hash#orig_symbolize_keys! , nil key   3.510000   0.170000   3.680000 (  3.720439)
Hash#symbolize_keys! , nil key        0.360000   0.000000   0.360000 (  0.392987)
Hash#orig_symbolize_keys!             2.020000   0.080000   2.100000 (  2.168747)
Hash#symbolize_keys!                  0.360000   0.010000   0.370000 (  0.371135)
-------------------------------------------------------------- total: 6.510000sec

                                          user     system      total        real
Hash#orig_symbolize_keys! , nil key   3.390000   0.160000   3.550000 (  3.551547)
Hash#symbolize_keys! , nil key        0.350000   0.000000   0.350000 (  0.361843)
Hash#orig_symbolize_keys!             3.400000   0.160000   3.560000 (  3.571425)
Hash#symbolize_keys!                  0.360000   0.000000   0.360000 (  0.362906)

hash_symbolize_keys.diff

From b57634fcbdab7526965a0b05b39f55ef76451cc5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lourens=20Naud=C3=A9?= <lourens@methodmissing.com>
Date: Sun, 7 Feb 2010 23:20:37 +0000
Subject: [PATCH] Hash#symbolize_keys(!) optimizations

---
 .../lib/active_support/core_ext/hash/keys.rb       |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/activesupport/lib/active_support/core_ext/hash/keys.rb b/activesupport/lib/active_support/core_ext/hash/keys.rb
index 045a694..62990f7 100644
--- a/activesupport/lib/active_support/core_ext/hash/keys.rb
+++ b/activesupport/lib/active_support/core_ext/hash/keys.rb
@@ -22,7 +22,7 @@ class Hash
   # to +to_sym+.
   def symbolize_keys!
     keys.each do |key|
-      self[(key.to_sym rescue key) || key] = delete(key)
+      self[key.to_sym] = delete(key) if key.respond_to?(:to_sym)
     end
     self
   end
-- 
1.6.4.4