class Grape::Util::StackableValues

def [](name)
  inherited_value = @inherited_values[name]
  new_value = @new_values && @new_values[name]
  return new_value || EMPTY unless inherited_value
  concat_values(inherited_value, new_value)
end

def []=(name, value)
  @new_values ||= {}
  @new_values[name] ||= []
  @new_values[name].push value
end

def concat_values(inherited_value, new_value)
  return inherited_value unless new_value
  inherited_value + new_value
end

def to_hash
  keys.to_h do |key|
    [key, self[key]]
  end
end