Especially since the second example only gives you a stringly-typed error.
If you want to add 'proper' error types, wrapping them is just as difficult in Go and Rust (needing to implement `Error` in Go or `std::Error` in Rust). And, while we can argue about macro magic all day, the `thiserror` crate makes said boilerplate a non-issue and allows you to properly propagate strongly-typed errors with context when needed (and if you're not writing library code to be consumed by others, `anyhow` helps a lot too).
fmt.Errorf with %w directive in fact wraps an error. It will return an fmt.wrapError struct which can be inspected using `errors.Is`. So it's not stringly typed anymore.
I am fully aware of how fmt.Errorf works as well as what's inside the `errors` package in the Golang stdlib, as I do work with the language regularly.
In practice, this ends up with several issues (and I'm just as guilty of doing a bunch of them when I'm writing code not intended for public consumption, to be completely fair).
fmt.Errorf is stupid easy to use. There's a lot of Go code out there that just doesn't use anything else, and we really want to make sure we wrap errors to provide 'context' since there's no backtraces in errors (and nobody wants to force consuming code to pay that runtime cost for every error, given there's no standard way to indicate you want it).
errors.New can be used to create very basic errors, but since it gives you a single instance of a struct implementing `error` there's not a lot you can do with it.
The signature of a function only indicates that it returns `error`, we have to rely on the docs to tell users what specific errors they should expect. Now, to be fair, this is an issue for languages that use exception's - checked exceptions in Java notwithstanding.
Adding a new error type that should be handled means that consumers need to pay attention to the API docs and/or changelog. The compiler, linters, etc don't do anything to help you.
All of this culminates to an infuriating, inconsistent experience with error handling.
I don't agree. There isn't a standard convention for wrapping errors in Rust, like there is in Go with fmt.Errorf -- largely because ? is so widely-used (precisely because it is so easy to reach for).
The proof is in the pudding, though. In my experience, working across Go codebases in open source and in multiple closed-source organizations, errors are nearly universally wrapped and handled appropriately. The same is not true of Rust, where in my experience ? (and indeed even unwrap) reign supreme.
> There isn't a standard convention for wrapping errors in Rust
I have to say that's the first time I've heard someone say Rust doesn't have enough return types. Idiomatically, possible error conditions would be wrapped in a Result. `foo()?` is fantastic for the cases where you can't do anything about it, like you're trying to deserialize the user's passed-in config file and it's not valid JSON. What are you going to do there that's better than panicking? Or if you're starting up and can't connect to the configured database URL, there's probably not anything you can do beyond bombing out with a traceback... like `?` or `.unwrap()` does.
For everything else, there're the standard `if foo.is_ok()` or matching on `Ok(value)` idioms, when you want to catch the error and retry, or alert the user, or whatever.
But ? and .unwrap() are wonderful when you know that the thing could possibly fail, and it's out of your hands, so why wrap it in a bunch of boilerplate error handling code that doesn't tell the user much more than a traceback would?
One would still use `?` in rust regardless of adding context, so it would be strange for someone with rust experience to mention it.
As for the example you gave:
File::create("foo.txt")?;
If one added context, it would be
File::create("foo.txt").context("failed to create file")?;
This is using eyre or anyhow (common choices for adding free-form context).
If rolling your own error type, then
File::create("foo.txt").map_err(|e| format!("failed to create file: {e}"))?;
would match the Go code behavior. This would not be preferred though, as using eyre or anyhow or other error context libraries build convenient error context backtraces without needing to format things oneself. Here's what the example I gave above prints if the file is a directory:
Error:
0: failed to create file
1: Is a directory (os error 21)
Location:
src/main.rs:7
My experience aligns with this, although I often find the error being used for non-errors which is somewhat of an overcorrection, i.e. db drivers returning “NoRows” errors when no rows is a perfectly acceptable result of a query.
It’s odd that the .unwrap() hack caused a huge outage at Cloudflare, and my first reaction was “that couldn’t happen in Go haha” but… it definitely could, because you can just ignore returned values.
But for some reason most people don’t. It’s like the syntax conveys its intent clearly: Handle your damn errors.
yeah but which is faster and easier for a person to look at and understand. Go's intentionally verbose so that more complicated things are easier to understand.
What's the "?" doing? Why doesn't it compile without it? It's there to shortcut using match and handling errors and using unwrap, which makes sense if you know Rust, but the verbosity of go is its strength, not a weakness. My belief is that it makes things easier to reason about outside of the trivial example here.
If you reject the concept of a 'return on error-variant else unwrap' operator, that's fine, I guess. But I don't think most people get especially hung up on that.
> What's the "?" doing? Why doesn't it compile without it?
I don't understand this line of thought at all. "You have to learn the language's syntax to understand it!"...and so what? All programming language syntax needs to be learned to be understood. I for one was certainly not born with C-style syntax rattling around in my brain.
To me, a lot of the discussion about learning/using Rust has always sounded like the consternation of some monolingual English speakers when trying to learn other languages, right down to the "what is this hideous sorcery mark that I have to use to express myself correctly" complaints about things like diacritics.
I don't really see it as any more or less verbose.
If I return Result<T, E> from a function in Rust I have to provide an exhaustive match of all the cases, unless I use `.unwrap()` to get the success value (or panic), or use the `?` operator to return the error value (possibly converting it with an implementation of `std::From`).
No more verbose than Go, from the consumer side. Though, a big difference is that match/if/etc are expressions and I can assign results from them, so it would look more like
let a = match do_thing(&foo) {
Ok(res) => res,
Err(e) => return e
}
instead of:
a, err := do_thing(foo)
if err != nil {
return err // (or wrap it with fmt.Errorf and continue the madness
// of stringly-typed errors, unless you want to write custom
// Error types which now is more verbose and less safe than Rust).
}
I use Go on a regular basis, error handling works, but quite frankly it's one of the weakest parts of the language. Would I say I appreciate the more explicit handling from both it and Rust? Sure, unchecked exceptions and constant stack unwinding to report recoverable errors wasn't a good idea. But you're not going to have me singing Go's praise when others have done it better.
Do not get me started on actually handling errors in Go, either. errors.As() is a terrible API to work around the lack of pattern matching in Go, and the extra local variables you need to declare to use it just add line noise.
