1 files changed, 50 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/ordered_hash.rb b/activesupport/lib/active_support/ordered_hash.rb
new file mode 100644
index 0000000000..5758513021
--- /dev/null
+++ b/activesupport/lib/active_support/ordered_hash.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+require "yaml"
+
+YAML.add_builtin_type("omap") do |type, val|
+  ActiveSupport::OrderedHash[val.map { |v| v.to_a.first }]
+end
+
+module ActiveSupport
+  # DEPRECATED: <tt>ActiveSupport::OrderedHash</tt> implements a hash that preserves
+  # insertion order.
+  #
+  #   oh = ActiveSupport::OrderedHash.new
+  #   oh[:a] = 1
+  #   oh[:b] = 2
+  #   oh.keys # => [:a, :b], this order is guaranteed
+  #
+  # Also, maps the +omap+ feature for YAML files
+  # (See http://yaml.org/type/omap.html) to support ordered items
+  # when loading from yaml.
+  #
+  # <tt>ActiveSupport::OrderedHash</tt> is namespaced to prevent conflicts
+  # with other implementations.
+  class OrderedHash < ::Hash
+    def to_yaml_type
+      "!tag:yaml.org,2002:omap"
+    end
+
+    def encode_with(coder)
+      coder.represent_seq "!omap", map { |k, v| { k => v } }
+    end
+
+    def select(*args, &block)
+      dup.tap { |hash| hash.select!(*args, &block) }
+    end
+
+    def reject(*args, &block)
+      dup.tap { |hash| hash.reject!(*args, &block) }
+    end
+
+    def nested_under_indifferent_access
+      self
+    end
+
+    # Returns true to make sure that this hash is extractable via <tt>Array#extract_options!</tt>
+    def extractable_options?
+      true
+    end
+  end
+end