Ensure `HashWithIndifferentAccess#transform_keys` to return `HashWithIndifferentAccess`

Currently, `#transform_values`, `#select` and `#reject` return instance
of `HashWithIndifferentAccess`. But `#transform_keys` returns instance
of Hash. This behavior is a bit confusing.

I think that `HashWithIndifferentAccess#transform_keys` should also return
instance of `HashWithIndifferentAccess` as well as other methods.

1 files changed, 5 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/hash_with_indifferent_access.rb b/activesupport/lib/active_support/hash_with_indifferent_access.rb
index 12291af443..fcc13feb8c 100644
--- a/activesupport/lib/active_support/hash_with_indifferent_access.rb
+++ b/activesupport/lib/active_support/hash_with_indifferent_access.rb
@@ -306,6 +306,11 @@ module ActiveSupport
       dup.tap { |hash| hash.transform_values!(*args, &block) }
     end
 
+    def transform_keys(*args, &block)
+      return to_enum(:transform_keys) unless block_given?
+      dup.tap { |hash| hash.transform_keys!(*args, &block) }
+    end
+
     def compact
       dup.tap(&:compact!)
     end