[simion314]

Question, if you are a library/program author why would you intentionally use a panic and not cleanup and return an error? Maybe I misunderstood and in fact good developers never trigger panics unless there is no way to avoid it, like if they could not prevent it with more checks or is it impossible to cleanup because they already fucked up, wrote garbage in the process memory and safest thing is to kill the process.

[oconnor663]

I think there are a few cases where Rust likes to panic, but different people probably have different opinions here:

- Extremely common operations with dedicated syntax, where introducing error handling would be burdensome. Things like array indexing or arithmetic overflow. In these cases, you usually want an alternative, fallible way to do the same operation.

- Cases where most callers will probably convert the error into a panic anyway. One example of this might be .split_at() on slices, which is bounds-checked just like an array access. Most callers would probably just .unwrap() the out-of-bounds case, and callers who don't want it to panic can easily check before the call, so it's more ergonomic to panic.

- Cases where the only plausible reason for failure is a bug in the caller. For example, the .borrow() and .borrow_mut() methods on RefCell will panic if a write overlaps with another read or write. The caller is almost always expected to statically guarantee that that doesn't happen, usually by making all borrows short-lived. (And here again there are fallible alternatives available.)

An interesting example of something that doesn't panic, but which probably should, is taking a mutex. The standard mutex in Rust includes a "poisoning" mechanism, which almost every caller just .unwrap()s. I think the majority opinion these days is that poisoning should just be removed, but given that it's around I think most people wish it just panicked instead of returning a Result.

[notriddle]

> is it impossible to cleanup because they already fucked up, wrote garbage in the process memory and safest thing is to kill the process

That’s essentially it, yes. My code should never actually panic. If it does, it means the state of the process has become deeply diseased, and attempting to “clean up” is likely to just make things worse. Of course, if it’s safe Rust, then it still won’t write past the end of a buffer or anything disastrous like that, but buggy code is still buggy code and there’s lots of stuff Rust won’t stop you from doing.

One of the more extreme things I’ve done in production Rust code was add a “watchdog thread”. It has a channel that takes unit and receives on a timeout, and the thread doing the actual work is expected to send it a message once a minute. If it doesn’t receive a message within a minute, it hard aborts the process. The default setup is run under a service manager like systemd to make sure it gets restarted, and that failures are actually logged somewhere.

This is meant to solve the problem that safe Rust is a Turing complete language, so is subject to the halting problem. The type checker can prove that you won’t read past the end of a buffer, but it cannot prove that your code will ever actually finish running. Which means, if you have a project like a web scraper that needs high uptime, you need to prevent it from getting stuck somehow.

[simion314]

I agree, so Am I wrong or the issue seems to be community culture thing, where some developers panic too eagerly? Say I make a library for resizing images and I have one public function resizeImage(options) , a good developer would think that maybe my code code has a bug and some function from standard library would panic, I should ensure I catch this and my public function never panics (even if there is no memory,disk or whatever Ias an author I should try not to intentionally panic" where a bad Rust developer thinks like " this will never panic unless I made a bug, if I amde a bug I am happy to panic and crush some sucker program so I get the bug report and fix the bug".

There are always bugs(logic bugs where Rust can't protect you) so why not have a clean interface?

[Georgelemental]

IO errors like running out of disk space would be handled by returning a `Result` type, not by panicking. Often, Rust code/libraries panic on out-of-memory errors because recovering from that isn't a priority for most application code. But if you are writing lower-level or high-reliability code and you do want to handle out-of-memory errors, the Rust standard library (and many third-party libraries) offer alternative fallible memory allocation APIs that return `Result` instead of panicking on out-of-memory.

[notriddle]

I disagree.

A good developer will crash the program, as soon as possible, if and only if it has a bug. If you want to write a program that never crashes, then you need to write a program with no bugs.

The reason you don’t want buggy code to limp along after it detects a bug, is that crashing isn’t the worst possible thing.

The worst possible thing is getting stuck in an infinite loop or a deadlock.