pub unsafe extern fn rocksdb_mergeoperator_create(state: *mut c_void, destroy: extern fn(*mut c_void), full_merge: extern fn(arg: *mut c_void, key: *const c_char, key_len: size_t, existing_value: *const c_char, existing_value_len: size_t, operands_list: *const *const c_char, operands_list_len: *const size_t, num_operands: c_int, success: *mut u8, new_value_length: *mut size_t) -> *const c_char, partial_merge: extern fn(arg: *mut c_void, key: *const c_char, key_len: size_t, operands_list: *const *const c_char, operands_list_len: *const size_t, num_operands: c_int, success: *mut u8, new_value_length: *mut size_t) -> *const c_char, delete_value: Option<extern fn(*mut c_void, value: *const c_char, value_len: *mut size_t)>, name_fn: extern fn(*mut c_void) -> *const c_char) -> DBMergeOperator