mea_rah , 5 months ago (edited 5 months ago)

You can bubble up the Error with ?operator. It just has to be explicit (function that wants to use ? must return Result) so that the code up the stack is aware that it will receive Result which might be Err. The function also has defined Error type, so you know exactly which errors you might receive. (So you're not surprised by unexpected exception type from somewhere deep in the call stack. Not sure about Java, but in Python that is quite a pain)

Edit: To provide an example for the mentioned db fetch. Typically your query function would return Result(Option). (So Err if there was error, Ok(None) if there was no error, but query returned no results and Ok(Some(results)) if there were results)
This is pretty nice to work with, because you can distinguish between "error" and "no resurts" if you want, but you can also decide to handle these same way with:

query()
  .unwrap_or(None)
  .iter().map(|item| do_thing(item))

So I have the option to handle the error if it's something I can handle and then the error handling isn't standing in my way. There are no try-catch blocks, I just declare what to (not) do with the error. Or I can decide it's better handled up the stack:

query()?
  .iter().map(|item| do_thing(item))

This would be similar to exception bubbling up, but my function has to explicitly return Result and you can see in the code where the "exception" is bubbled up rather than bubbling up due to absence of any handler. In terms predictability I personally find this more predictable.