pub unsafe extern "C" fn partial_merge_callback<F: MergeFn, PF: MergeFn>(
raw_cb: *mut c_void,
raw_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,
) -> *mut c_char