Unrecoverable errors are things like stack overflows or out of bounds array access. There is no reasonable way to soldier on after this, so the program should just end. Trying to continue the program in such situations only leads to pain. Like array accesses out of bounds that allow you to read unrelated memory.
But it’s still an evolving area. For example, failure to allocate memory - is that recoverable or unrecoverable? Initially it was thought that it was unrecoverable, and programs would panic if memory failed to allocate. This seemed reasonable, until folks tried to use Rust within the Linux kernel. Within the kernel, failure to allocate memory is recoverable. Rust is evolving the semantics here.
All this to say, yes, Rust does allow you to define functions that either fail in a recoverable way, in which case the calling function should handle it. Or they fail in an unrecoverable way in which case there’s nothing the calling function can do to recover. Thankfully, panics in third party code are relatively rare so this doesn’t happen in practice.
No, I wholeheartedly disagree with this. It's the equivalent of exit(1) some way down the stack. Whats recoverable or not depends on the use case and is a decision to be made by the caller of a function, not the implementor.
Otherwise I agree with you, that library code should not fail/crash/exit(1) just because of some judgement about recoverability, and out to clean up after itself before passing control back to the caller. If the user wants to fix some ENOSPC deep in my library by shelling out to "rm -rf /" and then trying again, that's fine by me, and this should be reflected in the API.
Do you mean that e.g. an out-of-bounds error will panic? If that's the case, you can always access arrays/slices with some checked access, that will return a Result/Option and cannot panic. But it would be a PITA if you couldn't skip that.
Usually your HTTP framework will already have this implemented, i.e. a panic in a request handler will be "caught", converted to some 500 response, and should not affect other requests.
Other points of "catch all errors" don't need that. And then there are a lot of places where you do handle errors, if they are conceptually a Result. I know you can just catch SpecificError, but the ergonomics are just horrible in terms of control flow.
> there are a lot of places where you do handle errors, if they are conceptually a Result
Yet, what's conceptually a result lies in the eye of the beholder, and should not be dictated by an API designer IMHO. Rust's ? is a step in the right direction, but I'd argue since you care about specific errors in maybe 0.1% of invocations tops (in production code), and that's a stretch, the ? should actually work the other way round. And if the mechanism does not provide a way to select specific errors (such as a proper catch clause) the errors it exposes as a result should include runtime errors as well.
- You say there is no difference between unchecked exceptions and Go's errors
- I say yes there is since Go forces users to handle errors explicitly
- You say that's not technically true in all cases.
Where do I say that? I say that Go programmers, in 99.9% of cases, do manually what exceptions do automatically. In terms of cumbersome, error values are the equivalent of checked exceptions. The equivalent of runtime exceptions are panics.
> Go programmers, in 99.9% of cases, do manually what exceptions do automatically
Our experience working with Go must be very different.
Grepping for "err := " and looking at the first 10 results in my team's codebase.
* 4 cases where the error is just returned
* 1 case where the error is returned only if it matches a certain type (otherwise logged)
* 1 case where the error is logged as a warning.
* 1 case where the error is logged, some metric is incremented, and then execution continues as usual. (a fail-open authentication check)
* 1 case where the error is returned as different error type.
* 1 case where the error is returned, but only after accessing the result (this is a strange design / antipattern), and annotating it with a human-readable explanation.
* 1 case where the error is treated as a boolean condition, and is not returned. (the error condition is "does not exist").
(Obviously, without source code access the following is guesswork) The other cases might either not be required (since you'll get a stacktrace anyway and don't need to leave breadcrumbs) or be part of some general infrastructure, say interceptor, that logs interesting things on boundaries. At least that's my day to day experience comparing Go and Java.