Add `Hash#map_values` to ActiveSupport

Didn't get a chance to convert existing code, I'll skim through the code
base to make use of this later this afternoon.

2 files changed, 22 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/core_ext/hash.rb b/activesupport/lib/active_support/core_ext/hash.rb
index f68e1662f9..af4d1da0eb 100644
--- a/activesupport/lib/active_support/core_ext/hash.rb
+++ b/activesupport/lib/active_support/core_ext/hash.rb
@@ -6,3 +6,4 @@ require 'active_support/core_ext/hash/indifferent_access'
 require 'active_support/core_ext/hash/keys'
 require 'active_support/core_ext/hash/reverse_merge'
 require 'active_support/core_ext/hash/slice'
+require 'active_support/core_ext/hash/transform_values'
diff --git a/activesupport/lib/active_support/core_ext/hash/transform_values.rb b/activesupport/lib/active_support/core_ext/hash/transform_values.rb
new file mode 100644
index 0000000000..6ff7e91212
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/hash/transform_values.rb
@@ -0,0 +1,21 @@
+class Hash
+  # Returns a new hash with the results of running +block+ once for every value.
+  # The keys are unchanged.
+  #
+  #   { a: 1, b: 2, c: 3 }.transform_values { |x| x * 2 }
+  #   # => { a: 2, b: 4, c: 6 }
+  def transform_values(&block)
+    result = self.class.new
+    each do |key, value|
+      result[key] = yield(value)
+    end
+    result
+  end
+
+  # Destructive +transform_values+
+  def transform_values!
+    each do |key, value|
+      self[key] = yield(value)
+    end
+  end
+end