'Sloppy' std::map and std::pair: maps and pairs where the key or the first element is an std::string can optionally be saved / loaded as maps if supported by the data format. For example:
std_map:

key: value

instead of
std_map:

first: key

second: value
'Polymorphic' configurations: ariles::Any class defined in ariles/types.h provides functionality similar to protobuf::Any – this class automatically instantiates and reads configuration of some user-defined class based on its string id and stores a pointer to its base class. See tests/api_v2/types/any.h for an example.