"For the foreseeable future, the Go team will stop pursuing syntactic language changes for error handling. We will also close all open and incoming proposals that concern themselves primarily with the syntax of error handling, without further investigation.”
Personally I'm OK with this, I didn't see any of the (many) proposals as a definite improvement. They all had trade-offs.
Moreover, the "obvious" solution, i.e. treating (T,error) returns the same as Result<T,E>, does not actually work. The problem is that (T,error) behaves like a product type while Result<T,E> is a sum type and yes, some Go code does (ab)use this. In particular, the io.Reader.Read method in the standard library allows implementers to return (n>0,io.EOF), which has no equivalent Result representation. Many people consider this allowance to be a mistake, but it's too late to change it.
I kind of want to leave it there. But that will probably be looked on disfavorably.
I've seen at least a dozen attempts. It's not like it's hard to write it out. There's maybe a couple of variants but they're all just a handful of lines. The problem is, once you have an Option in hand, you end up trading:
val, err := whatever(...)
if err != nil {
// handle error
}
// use val
for val := whatever(...)
if err, isErr := val.Error(); isErr {
// handle error
}
realVal := val.Value()
// use realVal
What you win in nominal safety, you're definitely losing in convenience.There's also no win in trying to offer a monadic interface like
finalVal := whatever(...).OnVal(func (val Value) opt.Option[Result] {
// use val
})
because that's the minimal specification of an anonymous function in Go, so it's very inconvenient. Even if that was trimmed down, nested functions are still problematic in other ways. And you still have to unpack finalVal anyhow.Really the solution is, install golangci-lint, turn on errcheck [1], use a pre-commit hook to make it a commit failure if golangci-lint fires, and that pretty much covers the problem in practice.
One of the problems with Option/Result/etc. advocacy... not the pattern itself, the advocacy... is that it is generally are presented, implicitly or explicitly, as if the alternative is C, with its errno and the need to not just check an error value, but remember to go actively seeking out errors constantly, making it easy to forget. But by modern standards, that's completely pathological.
If we rate error handling techniques on a scale from 1 to 10 (best), C here is a 1, and standard Option is maybe an 8 or a 9. The way Go does it is maybe a 6; it is completely true that you can neglect to handle an error (see errcheck comment in previous paragraph), but it is in your face that an error is possible, and that's really most of the problem. Putting Option/Result/etc. is not always a "go from 1 to 9" result. "Go from 6 to 8" is a much less impressive proposition, and the other inconveniences that come with it in Go tend to overwhelm the gain. I use errcheck all the time, and even in the Before Times when I was writing it all by hand it really didn't fire all that often. Especially if I exclude test code. In an AI era this hardly rates at all. AI never neglects the error.
Whether it does the right thing with it, now... that's another story entirely.
Read those error handling clauses if you're writing Go with AI. I really don't like what I've seen AIs do with them by default. What I've seen out of AI has been very thoughtless. Nominally correct in some weak sense, but thoughtless.
[1]: https://golangci-lint.run/docs/linters/configuration/#errche...
But in the cases I do want to catch a specific error, the signature only tells me that a function returns an error, not which type. So I do feel that returning (int, error) is strictly worse than Java's checked exceptions if you care about errors.
If instead of just returning (int, error) the function would return (int, parseError | outOfBoundsError) you would know that the parser function can fail on reading a number at all and on the number being to big/small to fit the type and handle then accordingly.
Saliently, Java in a sense has supported sum types in the throws declaration and the subsequent catch statements forever. Unfortunately it has not landed in other places where you can use types so you cannot use it for returning errors. Scala 3 supports this but has tiny adoption it seems.
Nor does that help with documentation, I'm guessing if I read a file then it might raise the error that the file does not exist. But what exactly is the technical type of that error? You have to search through the function's implementation, and functions that function calls, etc., to find out.
And it doesn't help with refactoring. If you create new.FileNotFoundError and change your function to return it, existing code which checks for old.FileNotFoundError will start to silently fail.
Thanks so much for that! Now I have no choice but to be reactive when something fails…
There’s also convenience at the returning side. You can always just return the error, and not have to care about dummy values for the other return values (which is especially annoying when changing the returned types).
That said, it might still not be worth the added complexity.
The err != nil quickly turns into metrics, logs, fallback strategies, retry mechanisms, flight recording, rate limiting, updating caches, so on.
Anyone who’s trying to shorten this hasn’t maintained any actual real software.