Function protobuf::reflect::accessor::make_singular_message_accessor

pub fn make_singular_message_accessor<M: Message + 'static, F: Message + 'static>(name: &'static str,
                                                                                  has: fn(&M) -> bool,
                                                                                  get: fn<'a>(&'a M) -> &'a F)
                                                                                  -> Box<FieldAccessor + 'static>