class Google::Protobuf::FieldDescriptor

def set_value_on_message(value, msg, arena, wrap: false)
  message_to_alter = msg
  field_def_to_set = self
  if map?
    raise TypeError.new "Expected map" unless value.is_a? Google::Protobuf::Map
    message_descriptor = subtype
    key_field_def = Google::Protobuf::FFI.get_field_by_number(message_descriptor, 1)
    key_field_type = Google::Protobuf::FFI.get_type(key_field_def)
    raise TypeError.new "Map key type does not match field's key type" unless key_field_type == value.send(:key_type)
    value_field_def = Google::Protobuf::FFI.get_field_by_number(message_descriptor, 2)
    value_field_type = Google::Protobuf::FFI.get_type(value_field_def)
    raise TypeError.new "Map value type does not match field's value type" unless value_field_type == value.send(:value_type)
    raise TypeError.new "Map value type has wrong message/enum class" unless value_field_def.subtype == value.send(:descriptor)
    arena.fuse(value.send(:arena))
    message_value = Google::Protobuf::FFI::MessageValue.new
    message_value[:map_val] = value.send(:map_ptr)
  elsif repeated?
    raise TypeError.new "Expected repeated field array" unless value.is_a? RepeatedField
    raise TypeError.new "Repeated field array has wrong message/enum class" unless value.send(:type) == type
    arena.fuse(value.send(:arena))
    message_value = Google::Protobuf::FFI::MessageValue.new
    message_value[:array_val] = value.send(:array)
  else
    if value.nil? and (sub_message? or !real_containing_oneof.nil?)
      Google::Protobuf::FFI.clear_message_field message_to_alter, field_def_to_set
      return true
    end
    if wrap
      value_field_def = Google::Protobuf::FFI.get_field_by_number subtype, 1
      type_for_conversion = Google::Protobuf::FFI.get_c_type(value_field_def)
      raise RuntimeError.new "Not expecting to get a msg or enum when unwrapping" if [:enum, :message].include? type_for_conversion
      message_value = convert_ruby_to_upb(value, arena, type_for_conversion, nil)
      message_to_alter = Google::Protobuf::FFI.get_mutable_message(msg, self, arena)[:msg]
      field_def_to_set = value_field_def
    else
      message_value = convert_ruby_to_upb(value, arena, c_type, subtype)
    end
  end
  Google::Protobuf::FFI.set_message_field message_to_alter, field_def_to_set, message_value, arena
end