←back to thread

Matt Godbolt sold me on Rust by showing me C++

(www.collabora.com)
611 points LorenDB | 4 comments | 06 May 25 17:51 UTC | HN request time: 0.315s | source
Show context
dvratil ◴[06 May 25 18:20 UTC] No.43908097[source]▶
The one thing that sold me on Rust (going from C++) was that there is a single way errors are propagated: the Result type. No need to bother with exceptions, functions returning bool, functions returning 0 on success, functions returning 0 on error, functions returning -1 on error, functions returning negative errno on error, functions taking optional pointer to bool to indicate error (optionally), functions taking reference to std::error_code to set an error (and having an overload with the same name that throws an exception on error if you forget to pass the std::error_code)...I understand there's 30 years of history, but it still is annoying, that even the standard library is not consistent (or striving for consistency).

Then you top it on with `?` shortcut and the functional interface of Result and suddenly error handling becomes fun and easy to deal with, rather than just "return false" with a "TODO: figure out error handling".

replies(24): >>43908133 #>>43908158 #>>43908212 #>>43908219 #>>43908294 #>>43908381 #>>43908419 #>>43908540 #>>43908623 #>>43908682 #>>43908981 #>>43909007 #>>43909117 #>>43909521 #>>43910388 #>>43912855 #>>43912904 #>>43913484 #>>43913794 #>>43914062 #>>43914514 #>>43917029 #>>43922951 #>>43924618 #
1. tomp ◴[07 May 25 11:53 UTC] No.43914514[source]▶
Did you ever actually program in Rust?

In my experience, a lot of the code is dedicated to "correctly transforming between different Result / Error types".

Much more verbose than exceptions, despite most of the time pretending they're just exceptions (i.e. the `?` operator).

Why not just implement exceptions instead?

(TBH I fully expect this comment to be downvoted, then Rust to implement exceptions in 10 years... Something similar happened when I suggested generics in Go.)

replies(1): >>43920280 #
2. nomel ◴[07 May 25 20:32 UTC] No.43920280[source]▶
I've only worked in exceptions, so I can't really comprehend the book-keeping required without them. To me it's a separation of concerns: the happy path only involves happy code. The "side channel" for the unhappy path is an exception, with an exception handler at a layer of the abstraction where it's meaningful, yet happy, code. By "happy" I mean code that's simply the direct practical work that's trying to accomplished something, so doesn't need to worry about when things go terribly wrong.

Being blind to the alternative, and mostly authoring lower level libraries, what's the benefit of not having exceptions? I understand how they're completely inappropriate for an OS, a realtime system, etc, but what about the rest? Or is that the problem: once you have the concept, you've polluted everything?

replies(2): >>43921024 #>>43921255 #
3. alpaca128 ◴[07 May 25 22:07 UTC] No.43921024[source]▶
In places where you only want to pass an error to the caller, Rust lets you just add "?" to the call that returns a Result/Option. And the Rust compiler will check that every potential error is handled.

I wouldn't say that it's the tedious part of the language.

4. tomp ◴[07 May 25 22:42 UTC] No.43921255[source]▶
There's mostly drawback of having exceptions, I'm not really aware of any benefits of not having them.

People often complain about:

- performance impact, either speed (most languages) or binary size (C++); this, however, is mostly an implementation concern, and doesn't impact Rust at all, as exceptions can simply be syntax-level compiler sugar, and can be compiled exactly the same as Result type is currently (having said that, the optional stack trace is another potential issue, which would have a performance impact even in Rust)

- checked exceptions - this is particularly a concern in Java, which has a fairly poor type system (closed subtyping only) and no type inference, so declaring all unhandled exceptions is tedious

- non-checked exceptions - in this case, "every exception can happen anywhere" so it's ostensibly unsafe (well it's just how life is, and even Java has special unchecked exceptions such as OutOfMemory that can happen anywhere) - some people claim that "exceptions can't just randomly jump out of code" is a benefit of not having exceptions but usually those people sweep OutOfMemory and DivisionByZero under the rug (e.g. Rust, where they just "crash" the program)

Rust would obviously fit the checked exceptions path, as the Result implementatoin basically is "poor-man's checked exceptions". It only needs to flip the syntax sugar - propagate by default (and implicitly), "catch" and materialize using `?` - as well as making Error an open enum (such that you can add cases implicitly - see e.g. OCaml's exception type `exn` [1]) - and that's basically it!

[1] https://ocaml.org/manual/5.3/extensiblevariants.html