ActiveSupport::OrderedHash 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 yaml.org/type/omap.html) to support ordered items when loading from yaml.

ActiveSupport::OrderedHash is namespaced to prevent conflicts with other implementations.

Methods
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Instance Public methods
encode_with(coder)
# File activesupport/lib/active_support/ordered_hash.rb, line 27
def encode_with(coder)
  coder.represent_seq '!omap', map { |k,v| { k => v } }
end
extractable_options?()

Returns true to make sure that this hash is extractable via Array#extract_options!

# File activesupport/lib/active_support/ordered_hash.rb, line 36
def extractable_options?
  true
end
nested_under_indifferent_access()
# File activesupport/lib/active_support/ordered_hash.rb, line 31
def nested_under_indifferent_access
  self
end
to_yaml_type()
# File activesupport/lib/active_support/ordered_hash.rb, line 23
def to_yaml_type
  "!tag:yaml.org,2002:omap"
end