Function duckdb_map_type_key_type 

pub unsafe extern "C" fn duckdb_map_type_key_type(
    type_: duckdb_logical_type,
) -> duckdb_logical_type

Retrieves the key type of the given map type.

The result must be freed with duckdb_destroy_logical_type

type: The logical type object returns: The key type of the map type. Must be destroyed with duckdb_destroy_logical_type.