[Manishearth]

> Rust's notoriously poor error messages

I've actually heard the opposite feedback; Rust's error messages try to be super helpful.

Note that concepts like ownership and Sync are new to most programmers, and it's impossible to explain them in an error message. This is where the extended error messages (via --explain) and the book come in.

The tutorial has this style because Rust espouses catching things at compile time, so the tutorial demonstrates this being done by doing the wrong thing a few times and reiterating why it gave an error.

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Could you give examples of confusing error messages? I'd love to improve them. The one you mention .... doesn't exist. This (http://is.gd/keukPm) is what that error message looks like, and (a) it mentions Sync, (b) it also mentions that `Arc<bool>` cannot be shared between threads safely.

If you were referring to "So, we need some type that lets us have more than one reference to a value and that we can share between threads, that is it must implement Sync." from the book, the last part about Sync has nothing to do with that error message. If you follow the book, the error message is clear without the context of threads -- `data` was moved into the first spawn() call and the subsequent ones can't use it. One does not conclude that Sync is necessary from this error message, and that's not what the book is trying to say.

This sentence is actually skipping a step, one like http://is.gd/RPNOm4, where the compiler asks you for a Send type (or a Sync type, depending on the exact code). Instead of stepping through this example, it just introduces Sync directly by noting that we're dealing with threads anyway and the reader already knows what Sync/Send are. It doesn't conclude that Sync is necessary from the error message.

> The bit about Mutex also has a "just type this to fix the problem with no explanation of how or why it works" flavour (although I guess if you already grok mutexes then its use here might be obvious to you).

The previous sentence says "for example a type that can ensure only one thread at a time is able to mutate the value inside it at any one time.", which is exactly what a mutex does. Unless you want a lower level explanation which IMO isn't necessary. It could explain locking more though; I'll fix that.

[firebones]

I've found the Rust compiler to provide very useful messages. That said, it does take a certain amount of experience in the language before you grok the terminology and appropriate remedies to overcome some compiler errors. As a beginner, I'd typically open about 5-10 different documentation, blog post, SO and tutorial pages to try to figure out what I was doing wrong. Once I understood the underlying concept, I could go back and understand what the compiler message was telling me, as plain as day. After awhile, I had a strong enough understanding of the borrow checker that I could usually interpret the compiler error messages in a pretty straightforward fashion. But it takes time if you're coming from a non C/C++ language!

If you're learning Rust, I would recommend tracing back every compiler error you encounter to this page [1] to see some other examples and resolutions (if the compiler's suggestions don't make it clear as to what to do). It's the most underrated page in the entire Rust documentation set, and could be the launch point for a lot of teaching and learning. Read the book to start, certainly (and the revisions Steve Klabnik has been making are very, very good), but that error index page is very valuable for the day to day issues.

Rust rewards gumption [2] and perseverance.

[1] https://doc.rust-lang.org/error-index.html [2] https://en.wikipedia.org/wiki/Gumption_trap

[Manishearth]

> you encounter to this page [1]

I love the extended errors. Note that you can just use `rustc --explain <error code>` without opening a web page, but of course it won't be formatted then.

> But it takes time if you're coming from a non C/C++ language!

Ultimately there's little substitute to learning the concepts behind the language :) Error-driven-development is fun, and quite useful once you know the language, but if used as the only way to learn the language it can be problematic. That said, I enjoy using errors to explain Rust concepts -- as long as you explain them. If a new user is hit with a steaming pile of errors you can't really expect them to understand it directly.

I have talked with a lot of folks coming from a non-systemsy background, and sort of have an idea of the things that get confusing (I once had similar problems when learning C++). I'm planning a blog post series (no ETA, pretty swamped with other work :/ ) that teaches both Rust (specifically, the safety bits like the borrow checker) and what's going on under the hood (regarding memory, the stack/heap, etc) using each as a crutch to explain the other in a leapfrog way, to introduce the language and low-level programming to folks coming from languages like JS.