2 files changed, 32 insertions, 5 deletions
diff --git a/activesupport/lib/active_support/core_ext/hash.rb b/activesupport/lib/active_support/core_ext/hash.rb
index 7d94d70910..2a99468b4e 100644
--- a/activesupport/lib/active_support/core_ext/hash.rb
+++ b/activesupport/lib/active_support/core_ext/hash.rb
@@ -1,8 +1,6 @@
-require File.dirname(__FILE__) + '/hash/keys'
-require File.dirname(__FILE__) + '/hash/indifferent_access'
-require File.dirname(__FILE__) + '/hash/reverse_merge'
-require File.dirname(__FILE__) + '/hash/conversions'
-require File.dirname(__FILE__) + '/hash/diff'
+%w(keys indifferent_access reverse_merge conversions diff slice).each do |ext|
+  require "#{File.dirname(__FILE__)}/hash/#{ext}"
+end
 
 class Hash #:nodoc:
   include ActiveSupport::CoreExtensions::Hash::Keys
@@ -10,4 +8,5 @@ class Hash #:nodoc:
   include ActiveSupport::CoreExtensions::Hash::ReverseMerge
   include ActiveSupport::CoreExtensions::Hash::Conversions
   include ActiveSupport::CoreExtensions::Hash::Diff
+  include ActiveSupport::CoreExtensions::Hash::Slice
 end
diff --git a/activesupport/lib/active_support/core_ext/hash/slice.rb b/activesupport/lib/active_support/core_ext/hash/slice.rb
new file mode 100644
index 0000000000..6fe5e05330
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/hash/slice.rb
@@ -0,0 +1,28 @@
+require 'set'
+
+module ActiveSupport #:nodoc:
+  module CoreExtensions #:nodoc:
+    module Hash #:nodoc:
+      # Slice a hash to include only the given keys. This is useful for
+      # limiting an options hash to valid keys before passing to a method:
+      #
+      #   def search(criteria = {})
+      #     assert_valid_keys(:mass, :velocity, :time)
+      #   end
+      #
+      #   search(options.slice(:mass, :velocity, :time))
+      module Slice
+        # Returns a new hash with only the given keys.
+        def slice(*keys)
+          allowed = Set.new(respond_to?(:convert_key) ? keys.map { |key| convert_key(key) } : keys)
+          reject { |key,| !allowed.include?(key) }
+        end
+
+        # Replaces the hash with only the given keys.
+        def slice!(*keys)
+          replace(slice(*keys))
+        end
+      end
+    end
+  end
+end