The type of the keys and the type of the infos is stated when the Mapping type is instantiated. A chained list is used. This implementation is advantageous to store some entries in a memory efficient way. For less than three entries the list version is about as fast as the hash implementation, access time for more entries increases linear. The memory usage is not constant per entry.
Less space is used, if the entries have the same types or lie in the same container.
A mapping with all inserted objects lying in the same container and with all keys of the same type uses 20 bytes of persistent memory per entry. An entry which key type, info type, key container and info container is different from the other entries uses 40 bytes of memory. This is the default implementation. The mapping starts with a list implementation to save memory usage. If the 12th entry is inserted, the implementation changes to the hash version.