class ActiveSupport::HashWithIndifferentAccess

hash.fetch_values('a', 'c') # => KeyError: key not found: "c"
hash.fetch_values('a', 'c') { |key| 'z' } # => ["x", "z"]
hash.fetch_values('a', 'b') # => ["x", "y"]
hash[:b] = 'y'
hash[:a] = 'x'
hash = ActiveSupport::HashWithIndifferentAccess.new

raises an exception when one of the keys can't be found.
Returns an array of the values at the specified indices, but also

def fetch_values(*indices, &block)
  super(*indices.map { |key| convert_key(key) }, &block)
end