>I've long faulted Rust's use of Result over exceptions
Why?
Why?
That said, I've spent too much of my life chasing implicit control flow to accept exceptions. Heck, C++'s "noexcept" is a strong argument against exceptions all by itself.
Exceptions came to be during the 1990's, as the C++ARM to C++98 standardisation process was taking place.
Naturally during the early days C++ compilers lacked exceptions, as CFront was introduced without them.
Then we had the C folks that were migrating to C++.
When C++ compilers finally supported exception, compilers vendors introduced the non standard switch to disable them, so that existing code could still compile with the expected behaviour.
The standard itself does not acknowledge this as allowed.
This feature was naturally misused by the anti-exception folks, same applies to how RTTI came to be.
So noexcept is a way to be able to write code to appease both camps, while surfacing what variant was chosen by the programmer.
From my point of view allowing disabling exceptions in first place was a mistake, those folks should have moved back to C, or fixed their code.
> result types pessimize code more
> They're arguably noisier at the source level too.
Yes. This is why unchecked exceptions are annoying. Checked exceptions are a „failed experiment“ anyway.
A result type (or even Go‘s err) with forced error handling meaningfully increases the robustness of a program in my experience.
I haven't written any Java since it has gained those, so I suspect there might be other aspects making it awkward. And it still would lack exhaustiveness checking that e.g. Rust has.
Unchecked exceptions lead to unhandled exceptions at runtime. We've all seen screens with Java programs running with tons of exceptions in the log, or worse, that crash with unhandled exceptions. This is the result of the unchecked exceptions mess, which is why I won't use languages that use them for routine error handling for anything more than trivial programs.
Exception handling is just annoying from a syntax perspective. Also checked Exceptions have the problem that they bubble up types that a different layer shouldn’t even be aware of due to exception chaining (cause of a cause etc), unless you carefully re-throw them, which nobody did.
Lower ceremony errors are just better to deal with.
https://smallcultfollowing.com/babysteps/blog/2024/05/02/unw...
use std::panic::catch_unwind;
fn throws_exception(){
panic!("hello");
}
fn main(){
match catch_unwind(|| {
throws_exception();
println!("Never reached");
}) {
Ok(_) => (),
Err(e) => println!(
"threw an exception: {:?}",
e.downcast_ref::<&'static str>().unwrap())
}
}
> I can disable exceptions in rustc, but I can't disable the influence they have on language and library design
It's the other way around. The fact that unwinding can be (and regularly is) trivially disabled is the ultimate motivator of why panics fundamentally cannot be used for error handling, and this is what influences language and library design (ultimately demanding `Result`-based error handling).
> Exceptions are the main reason you can't temporarily move something out from behind an exclusive reference, or return an error code from a Drop impl
No, this is absolutely untrue, and I'm not sure why you think this.
> Heck, Rust wouldn't even need destructors if it weren't for exceptions: the compiler could just tell you when you forgot to free something.
No, this is also untrue, and you appear to misunderstand the purpose of destructors. Feel free to provide code if you would like to try to make a more precise argument against unwinding.
Tomayto Tomahto.
> I have seen many Rust programs in my day, and not a single one has ever used `catch_unwind`
Yeah, cause it sucks. Hence my original point: all downsides and no benefits. Also how people use Rust's exceptions has no bearing on whether or not they are exceptions.
> The fact that unwinding can be (and regularly is) trivially disabled is the ultimate motivator of why panics fundamentally cannot be used for error handling
Unwinding can be disabled in C++, too. They still call them exceptions over there.
> you appear to misunderstand the purpose of destructors.
In a language with exceptions, destructors (or something similar like try-finally) are required to guarantee resource cleanup. In a language without exceptions, it is enough to simply write the cleanup code at scope exit points. Rust's static analysis is strong enough to ensure you do this correctly in the hypothetical world where the language does not have exceptions.
If your insinuation here is that I don't understand why you might still want destructors in the absence of exceptions, then you've missed my point.
> Feel free to provide code if you would like to try to make a more precise argument against unwinding.
I already linked the precise argument against unwinding. It's written by Niko Matsakis, one of the core Rust language designers. It explains both the "temporary move from behind an exclusive reference" point and the "return a value from a drop impl" point (which the article calls "must move").