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 if key.respond_to?(:to_sym)) || key] = delete(key)
    end
    self
  end
end

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

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

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! } } 
end  

hash_symbolize_keys.diff

From ef206f879b5bdae312847a256a987135cd2d4b73 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lourens=20Naud=C3=A9?= <[email protected]>
Date: Sun, 7 Feb 2010 22:48:21 +0000
Subject: [PATCH] Faster Hash#symbolize_keys!

---
 .../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..62b38fb 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 if key.respond_to?(:to_sym)) || key] = delete(key)
     end
     self
   end
-- 
1.6.4.4

results.txt

methodmissing:~ lourens$ ruby hash_bench.rb
Rehearsal -----------------------------------------------------------------------
Hash#orig_symbolize_keys! , nil key   3.510000   0.160000   3.670000 (  3.717758)
Hash#symbolize_keys! , nil key        0.690000   0.000000   0.690000 (  0.727905)
Hash#orig_symbolize_keys!             2.020000   0.090000   2.110000 (  2.103823)
Hash#symbolize_keys!                  0.580000   0.000000   0.580000 (  0.589944)
-------------------------------------------------------------- total: 7.050000sec

                                          user     system      total        real
Hash#orig_symbolize_keys! , nil key   3.490000   0.160000   3.650000 (  3.668927)
Hash#symbolize_keys! , nil key        0.690000   0.000000   0.690000 (  0.691079)
Hash#orig_symbolize_keys!             2.020000   0.080000   2.100000 (  2.125950)
Hash#symbolize_keys!                  0.600000   0.000000   0.600000 (  0.625422)