1 files changed, 55 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/object/deep_dup.rb b/activesupport/lib/active_support/core_ext/object/deep_dup.rb
new file mode 100644
index 0000000000..c66c5eb2d9
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/object/deep_dup.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require "active_support/core_ext/object/duplicable"
+
+class Object
+  # Returns a deep copy of object if it's duplicable. If it's
+  # not duplicable, returns +self+.
+  #
+  #   object = Object.new
+  #   dup    = object.deep_dup
+  #   dup.instance_variable_set(:@a, 1)
+  #
+  #   object.instance_variable_defined?(:@a) # => false
+  #   dup.instance_variable_defined?(:@a)    # => true
+  def deep_dup
+    duplicable? ? dup : self
+  end
+end
+
+class Array
+  # Returns a deep copy of array.
+  #
+  #   array = [1, [2, 3]]
+  #   dup   = array.deep_dup
+  #   dup[1][2] = 4
+  #
+  #   array[1][2] # => nil
+  #   dup[1][2]   # => 4
+  def deep_dup
+    map(&:deep_dup)
+  end
+end
+
+class Hash
+  # Returns a deep copy of hash.
+  #
+  #   hash = { a: { b: 'b' } }
+  #   dup  = hash.deep_dup
+  #   dup[:a][:c] = 'c'
+  #
+  #   hash[:a][:c] # => nil
+  #   dup[:a][:c]  # => "c"
+  def deep_dup
+    hash = dup
+    each_pair do |key, value|
+      if key.frozen? && ::String === key
+        hash[key] = value.deep_dup
+      else
+        hash.delete(key)
+        hash[key.deep_dup] = value.deep_dup
+      end
+    end
+    hash
+  end
+end