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

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611 points LorenDB | 3 comments | 06 May 25 17:51 UTC | HN request time: 0.001s | source
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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".

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1. bena ◴[06 May 25 20:09 UTC] No.43909117[source]▶
Ok, I'm at like 0 knowledge on the Rust side, so bear that in mind. Also, to note that I'm genuinely curious about this answer.

Why can't I return an integer on error? What's preventing me from writing Rust like C++?

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2. tczMUFlmoNk ◴[06 May 25 20:37 UTC] No.43909389[source]▶
You can write a Rust function that returns `i32` where a negative value indicates an error case. Nothing in Rust prevents you from doing that. But Rust does have facilities that may offer a nicer way of solving your underlying problem.

For instance, a common example of the "integer on error" pattern in other languages is `array.index_of(element)`, returning a non-negative index if found or a negative value if not found. In Rust, the return type of `Iterator::position` is instead `Option<usize>`. You can't accidentally forget to check whether it's present. You could still write your own `index_of(&self, element: &T) -> isize /* negative if not found */` if that's your preference.

https://doc.rust-lang.org/std/iter/trait.Iterator.html#metho...

3. bonzini ◴[06 May 25 20:45 UTC] No.43909468[source]▶
Nothing prevents you, you just get uglier code and more possibility of confusion.