Automatic stack capture for exceptions is something my language could conceivably do on my behalf.
Writing even 3 lines of code per function to propogate up the error is a huge pain, especially because it pollutes the return type -- MustWhatever() in go is much easier to use than Whatever() returning (type, err)
I guess it's part of the Go philosophy - more dynamic logging would most likely incur relatively higher performance costs.
The ? operator is better than nothing, but I still need my error types to match all the way up the stack
Forgetting that a function returns an error:
...
foo() // foo returns an error that isn't being handled.
...
...
err := foo()
err = bar() // The previous error will go unhandled.
...
...
if err != nil {
return nil
}
...
...
err := json.Unmarshal(bytes, &obj)
if err != nil {
return err // should be errors.WithStack(err)
}
...
I think there are a lot of schools of thought on this precisely because it is a difficult problem to solve: it requires getting a bunch of programmers to agree about how the edge cases should be handled, and that's no small feat.
Composition: Errors as values means it is easy to write functions to deal with them. Errors as exceptions means invoking special language constructs. And program termination doesn't compose well. Library authors always avoid panics. Generally only applications are good at deciding when to panic and when to catch a panic.
Hidden: how do you know if a function panics? If it returns an error, I see that in the type signature and I can be forced to handle it by linting tools. People seem to not like Javas checked exceptions, but I think that like most things Java it had to do with some of the implementation details, I think the concept is much preferable to hidden exceptions/panics.
For the socket disconnect for example, maybe a child process maintains a connection to the parent manager process. A socket disconnect is absolutely unexpected then and explicitly handling it adds noise.
You can reach out to us on slack (gorotisserie.slack.com/archives/CS13EC3T6) for additional comments and feedback. Thanks!
One other issue I've struggled with is in propagating errors across goroutines. If an error is created in the child routine, `runtime.Callers` doesn't include any stack frames from the parent. Assuming the parent wraps the error, it sounds like Eris would give you at least one line of the parent stack trace. Does it handle this specifically by including all of them?
It seems to have a bit of a cleaner presentation in the error stack -- Its an array, which feels nicer than a string.
It's just that she isn't a major goddess, and is famous only for her "apple of beauty" trick. And outside classical scholars, that's arguably via Principia Discordia.
So I'm curious.
func (t *Thing) Process(id int) (string, error) {
return "", fmt.Errorf("not implemented")
}
func (t *Thing) Process(id int) (string, error) {
dat, err := t.store.Read(id)
if err != nil {
return "", fmt.Errorf("error reading ID: %w", err)
}
cert, err := dat.ExtractCertificate()
if err != nil {
return "", fmt.Errorf("error extracting certificate: %w", err)
}
return cert.Name(), nil
}
func (t *Thing) Process(id int) (string, error) {
dat, _ := t.store.Read(id) // TODO: error handling
cert, _ := dat.ExtractCertificate() // TODO: error handling
return cert.Name(), nil
}
Even worse, with this style of programming, someone up the stack who would actually want to handle these errors has no mechanism to do, since you're returning the same type from both error cases. If they wanted to handle the certificate error but not the read error, they would have to parse the error message string, which is brittle. But if you did want to add appropriate context, your function would bloat even more. Not to mention that the standard library doesn't really help, since it generally doesn't define any specific error types to set up some patterns for this. Even in your example, from the start you assumed that your function can either succeed or fail in a generic way, you didn't think that the signature may want to encode multiple different error types, which is what GP was talking about when saying you can't usually think about the sad case before the happy case. Sure, if the extent to which you want to define sad case first is 'sad case can happen', you can.
Go's error handling strategy is its weakest aspect, and it is annoying to hear advocates pretend that Go is doing it right, when 90% of Go code is doing the same thing as 90% of exception-based code, just manually and with less helpful context for either logging or for the 10% of code which actually wants to handle errors.
You look at what I'm doing as a more tedious and error-prone version of exception bubbling, but that misses the forest for the trees. The whole point of doing it this way is to lift errors out of the shadows of the exception control flow path, and put them front-and-center in the actual logic of the application. Programming (in many domains) is error handling, the error handling is at least and arguably more important than the business logic.
I don't want exceptions. I do want this (or something like it).
> Even worse, with this style of programming, someone up the stack who would actually want to handle these errors has no mechanism to do, since you're returning the same type from both error cases.
As the author of this module, I get to decide what my callers are able to see. What I've written is (IMO) the most straightforward and best general-purpose example, where callers can still test for the wrapped errors if they need to. If it were important for callers to distinguish between Read and Certificate errors, I would use sentinel errors e.g. var ErrCert (if the details weren't important) or custom error types e.g. type CertificateError struct (if they were).
Adding this stuff isn't bloat. Again, it's just as important as the business code itself.
> Go's error handling strategy is its weakest aspect, and it is annoying to hear advocates pretend that Go is doing it right
In industry, considering languages an organization can conceivably hire for, and considering the general level of industry programmers -- programs written in Go are consistently in the top tier for reliability, i.e. fewest bugs in logic, and fewest crashes. Certainly more reliable than languages with similar productivity like Python, Ruby, Node, etc.
There are plenty of flaws in Go's approach to error handling -- I would love to have Option or Result types, for example -- but I think, judging by outcomes, it's pretty clear that Go is definitely doing something right.
And if you think about it, defining those operator is a good practice as it tells your program how to handle errors.
Places where that approach really sucks include web api routes (unless I haven't figured out a trick yet). For example, rocket defines Responder on Result so long as the ok and error variants both define it, but since a boxed error is erased it doesn't function correctly.
Citation needed. It may simply be that those code bases are doing relatively trivial work compared to large programs in other languages, where bugs are more likely to happen simply due to code size. Even in this thread another poster wrote:
> I've accidentally introduced way more bugs through Go style error handling than through Python style error handling.
I've seen production golang code where errors were being silently overwritten. Much, much worse than anything in Java or C# where exceptions are explicitly swallowed.
Again, if you had showed an example where something is actually being done with the errors, I would have agreed with you 100%. But when all that is being done is bubbling the errors, having this be done manually by the programmer (and read every time by the code reviewer) is both inefficient and error-prone. Not to mention that one of the first 'skills' I developed as a Go programmer was to ignore any block starting with 'if err != nil', since it appears so, so much in the code. It's not uncommon to have one function contain 10 different 'if err != nil { return nil, fmt.Errorf("Error doing X %v", err)}' for trivial logic (make 10 calls to some external service, abort if anything fails).
I don't have a problem with encoding errors in the function return type. But, coupled with Go's inability to abstract any kind of control flow, this error 'handling' strategy is almost as bad as C's. Other languages that don't offer exceptions avoid this problem with higher level control mechanisms, such as monads or macros.
Even worse, the Go designers recommend some horrible patterns [0], like Scan() not returning an error, but putting the scanner in an error state that all other Scanner functions respect, and having client code explicitly check for the Error() property of the scanner object at the end - preventing any generic tool from helping check whether you correctly handle errors in your code, and introducing an entirely different pattern.
And I don't know the source of your claim about Go's reliability, but all of the studies I have read comparing programming languages have found no or very little effect of the choice of language on overall number of bugs. One recent study [1] which included Go did have it as one of the more reliable languages (but behind Ruby, Perl or Clojure), but with a very minor overall effect, that may be explained by many factors other than error handling (they did not compare languages by this aspect).
Edit: And one minor point, but I did miss the %w in your example code, which does indeed make it possible for code consuming your errors to differentiate them. In my defense, this is a feature of the very newest version of Go only; and having the difference between a 'testable' error and a not testable one be %w vs %v in a format string seems a design decision particularly hostile to code review.
[0] https://blog.golang.org/errors-are-values
[1] https://www.i-programmer.info/news/98-languages/11184-which-...
And I yours, so it seems we're just at an impasse of opinion. That's fine. We can continue being productive in our own ways, and history will judge the superior approach, in whole or part.
Honestly though, I would prefer the uncaught exception case. When an uncaught exception is thrown, it's very clear you have an uncaught exception and you know exactly where it came from. In the examples I wrote, you will accidentally catch an error silently. You will never know if anything went wrong unless silently catching the error triggers an issue somewhere else. Even then, it's pretty hard to trace back the bug to the lack of error handling code somewhere else.
And... Woah. That's kind of horrifying to me (though I totally get the explicitness of it)... does this just mean liberal amounts of: thing != nil everywhere? Or is the rest of the memory management I guess, uhh.., good/magical enough you don't have to worry about it constantly in calls further down the stack if you've checked it once? Or are you always feeding the nil check beast?
Not to me.
The other two examples, I could maybe understand, but they still look pretty close to normal Go code. In the case where you forget to handle an error, you need to be able to recognize the absence of the error checking bit. It would be one thing if there was extra code that looked wrong, but looking for the absence of code makes it hard to spot.
In the case where you return nil, it looks exactly like a normal early-exit from a function. You need to be able to recognize that the code is not a normal early-exit, and that the three letters "err" were swapped for the three letters "nil".
Yes, it does. Whenever you call a function that can possibly fail, you are supposed to add:
if err != nil {
return err
}
> Or is the rest of the memory management I guess, uhh.., good/magical enough you don't have to worry about it constantly in calls further down the stack if you've checked it once?
I don't quite understand the question here. Are you asking about a performance impact of having nil checks everywhere? If I had to guess, I would think there's a negligible performance impact because the branch predictor will always predict the happy case. As for memory concerns, as long as you are in the happy case and returning nil, no memory needs to be allocated. It's the same reason null doesn't require any memory allocation in other languages.
I don’t think that’s what the parent meant by his question. He was asking if you have to add runtime checks all over to make sure any reference type isn’t nil; no, you don’t—you only add the checks for those for which nil is a valid state in the program (such as errors). If it’s an invalid state, it will panic because it’s an exceptional circumstance—a programmer error. This isn’t a defense of nil; only a clarification about how nil is dealt with. With this context, the rest of his question (the part you didn’t understand) becomes clearer.