[KirinDave]

I guess then I have to ask, why would try() make that worse?

Because I can't stand Golang error handling. It's repetitive, it's error prone, and other language features interact with it so that when you make a mistake it can be as hard as a double free to track down where the erroneous default value was introduced.

On the other hand, using Rust, Ocaml, F# or Haskell I understand how my code composed and I can be confident I can just use an error handling strategy. The only complexities appear, as with everyone else, when we have asynchronous code.

So I don't mean to disagree with your feelings, but they're sure not mine and they're part of why I don't use Golang. I was excited about try() because it at least addressed the most tedious part.

[natefinch]

Try makes it worse because it is so easy to miss when reading the code. Because it encourages nesting function calls, which is harder for a human to parse than separate statements across lines. Because it means you can exit the current function from the middle of a line of code, and what runs before or doesn't run before is based on order of operations rather than requiring the exit to be a statement on its own line whose order cannot be misunderstood. Because it discourages giving more information with an error, so instead of "failed to open config file: EOF", you just get the EOF.

Go's error handling isn't any more error prone that writing if statements for all the rest of your code. if err != nil is no different than if age < 18. Either one is a branch in the code. I can literally count on one hand the number of times in 6 years of full time go development that I've seen people miss writing the if err != nil.

Being explicit is good. Spreading out the logic is good. Cramming a lot of logic into one line is bad.... and that's the sole purpose of try.

Maybe there's another way to make error handling better in Go. I'm not averse to looking into that. But try wasn't it.

You're talking about writing if err != nil being tedious, but what about matching Results from Rust, isn't that tedious? What about writing proper catch blocks in java or C++ or python, isn't that tedious? It's all just logic.

[akavel]

Writing Go professionally for 4 years already and being a Go fanboy since 2009: while endorsing many benefits of "if err" blocks, I do very much have the following issues with them (in no specific order):

- It's hard to spot outliers. This leads to occasional bugs that tend to get easily overlooked in code review. Also, it makes code reading harder when an "if err" block is subtly different. The most common case here being "if err == nil" (sometimes bug, sometimes on purpose) - super hard to notice.

- You say you have seen missed "if err" blocks only a few times. I say that's 100% too many; every one of them in my experience was a subtle bug (possibly comparable to off-by-one errors in C).

- When I need to focus on understanding/analyzing the optimistic path in a fragment of code (always the first thing I do when reading), the everpresent "if err" blocks introduce tiresome visual noise and make the reading/grokking process slower and harder (having to constantly try and mentally filter out some 80% of what my eyes see).

[mikeschinkel]

Just curious. Do you have a vision for how Go could change to improve your issues? (One of the key problems is nobody could agree on a better approach...)

Also, what editor/IDE do you use? The reason I ask is because of this: https://youtrack.jetbrains.com/issue/GO-7747

[tsimionescu]

The difference with catch blocks in Java, C++ or Python is that you only need to write them when you actually have something g meaningful to do.

If you only need to propagate the error or cleanup resources then propagate the error, then all you would write is... Nothing. And cleanup+propagation is by far the most common error handling strategy. In Java and Python exceptions even add context for you automatically to help track down what happened.

[sagichmal]

One foundational principle of Go is that the sad path is at least as important, and maybe more important, than the happy path. The best Go programmers I know write the sad path of their programs first, and then backfill the happy-path logic. So:

> you only need to write [error checking] when you actually have something meaningful to do.

Although it's the subject of a lot of ridicule, `if err != nil { return err }` is actually bad Go code, and not often written by good Go programmers. Errors in Go are, at a minimum, annotated with contextual information before being returned. Frequently, they are programmed-with in other, more sophisticated ways, depending on the domain of the program.

Shifting your mindset to understand errors as something significantly more important than the off-gassing of your program's execution is worthwhile in general, and, in Go, fundamental.

[tsimionescu]

The fact that you need to add context to errors usually exacerbates the problem and makes it even harder to read the code. You often end up with

  err = doThing()
  if err! = nil {
    return errors.New("Error doing thing", err)
  }

This doesn't add any useful information for whoever is reading the code, it's just boilerplate that you learn to skip while reviewing, while hopefully not missing any important thing that does happen on the error path.

As for 'programming with the error', I would like to see an actual use case for constantly doing this, and why exceptions would prevent that pattern. The only one I can remember is something highlighted as a 'good practice' by Rob himself: write everything you want to a bufio.Writer, without checking the error messages, and then calling Flush and only then checking if maybe something failed. If this is good, safe, sad-path-first, errors-are-values style... then my taste in programming is obviously bad. Obviously, the same could be achieved with exceptions.

[nirui]

First, the signature for `errors.New` is `New(text string) error`. It won't take more parameters than that. So I guess you mean `fmt.Errorf`.

If above is true, then how about:

    err := renderTemplate()

    if err! = nil {
        return fmt.Errorf("Error rendering template: %s", err)
    }

The end error could then be something for example:

    Error rendering template: Compiler has failed: Cannot load template: File /tmp/test.tpl was not found
    ------------------------  -------------------  --------------------  --------------------------------
     |                         |                    |                     |
    Returned by that           |                    |                     |
    example                   Returned by the       |                     |
                              fictional compiler   Returned by the        |
                                                   fictional template    Returned by the fictional file 
                                                   Loader                reader

I didn't even twist your example, and yet you can already see more information. And with that information, even a user can understand what's going on clearly. So ... more useful?

[tsimionescu]

Oops, I forgot if errors.New takes the 'cause' as well.

Regarding you example: the code itself still contains redundant information for someone reading it. True, the error ends up being nicer, though I would argue that the user would have been better served with a simple 'failed to load template file: /tmp/test.tpl', no need to show the pseudo call stack (so, only the fictional template loader should have been wrapping the error,for this particular case). And for a developer, the full call stack may be more useful. Exceptions would give you both for free - a nice message that can be shared to the user by whoever caused the most understandable error, and a call stack that can be logged at the upper layer so developers can see it if a bug is logged, and get a much fuller context.

[mikeschinkel]

I would argue that if you are using boilerplate annotations, you are doing it wrong. If you really do not need to add context, don't add context. But in my code I find that I want to add context about 90% of the time.

But then I am super zealous about making sure my error messages understandable without the need to track down other information. For example, I want to know that (something like) "the config file needs group read permissions" not "file cannot be opened." But maybe others value ease of programming more than I do and are less concerned about error UX than I am?

[icebraining]

> `if err != nil { return err }` is actually bad Go code, and not often written by good Go programmers.

Like the people who wrote the Go stdlib? Because that's filled with those - just look at the net/* packages.

[sagichmal]

One distinction that is often made by core team members is that you only need to annotate errors at package boundaries, and that returning unannotated errors within a package is fine. But in most code, the packages are not so well-defined, or well-thought-out, or sacrosanct, that they represent a good proxy for annotation decisions.

I would much rather have an error with too much or duplicate annotation than one with not enough. And I would further argue that, yes, in the stdlib, errors are generally under-annotated.

[steev]

Legitimate question: then what does good Go code that is written by good Go programmers do/look like? Wrap `err` in `errors.New("some function failed", err)`?

[sagichmal]

At a minimum, an error should be logged with appropriate context and execution allowed to continue; or annotated and returned. Error annotation is currently best achieved with pkg/errors as e.g. `errors.Wrap(err, "error doing thing")`. (The xerrors suggestion of `fmt.Errorf("error doing thing: %w", err)` is awkward and hacky.)

Many programs can benefit from a more structured approach to error management. But once you get past the minimum (above) there's no one-size solution for what "a more structured approach" looks like. I really enjoy how upspin.io does their errors package, though it is somewhat esoteric. I'm also reading and generally liking how Cockroach does things, though I don't like the coupling to Protobufs.

[mikeschinkel]

Recently the Go team introduced the xerrors package for improved error management: https://godoc.org/golang.org/x/xerrors

So using these functions is becoming part of what good Go programmers do.

[qwsxyh]

That statement is still correct even in the context of the stdlib.

[VMG]

> Errors in Go are, at a minimum, annotated with contextual information before being returned.

What surprised me when I last wrote Go was that there was no out-of-the-box solution to adding a stack trace to the error.

[sagichmal]

Stack traces are, for me, too much noise, and not enough signal. I prefer reading annotations added (prefixed) by programmers deliberately. File and line information for the call stack leading to the error maybe provide value in the dev cycle (e.g. when fixing tests) but basically don't in logs in production.

This is all to say: I can understand why they aren't more naturally part of errors, and I think it also helps explain why they are part of panics.

And with all that said, I wouldn't object to making stack traces easier to add to errors, as long as it was opt-in.

[Cthulhu_]

Does anyone know if this was a conscious decision? I mean IIRC in Java you're generally discouraged from throwing errors for control flow because creating the stack trace is a relatively heavy process. In Go this is of less concern and returning an error is pretty normal for control flow (as in errors are expected, not exceptional), and you shouldn't have to worry that an error path would be 100x as expensive as a normal flow because a stack trace is being generated.

[EmpirePhoenix]

Java allows since ~a decade time to omit the generation of stacktraces, for exactly such cases

[ithkuil]

yeah; we're getting there though, see https://github.com/golang/go/wiki/ErrorValueFAQ

[mikeschinkel]

JMTCW, but since I generally program Go in GoLand with the debugger, I have full access to the stack all the time so I have not found this to be a major concern. But YMMV.

[nicoburns]

But the issue with this is that it can be hard to know what all the possible error conditions are, and thus whether you have anything meaningful to do.

Using Rust, which makes errors explicit like Go, has been eye-opening to me. My programs never crash because I've handled every error condition. No effort on my part. No tests needed.

[tsimionescu]

Java also makes you handle every possible error condition, unless of course you chose to use an escape hatch. Rust allows the same.

By the way, Go is much happier to crash than Java - for example, a simple array index out of range will cause a program crash in a typical Go program, where it would only cause a request failure in a typical Java program. Not sure how Rust handles this.

Finally, choose that isn't tested (manually or automatically) is very unlikely to work. Maybe you can guarantee it doesn't crash, which is a much weaker guarantee, but I doubt even fully proven code (like seL4) is all bug-free before ever being run.

[lllr_finger]

Rust's use of Result is very different from try/catch and exceptions in Java, even if you opt-in to checked exceptions. The big difference is ergonomics and what patterns are used in underlying libraries - opting out of the idiomatic way in Rust feels wrong if you try doing it.

Rust handles your out of range scenario the same way Go does.

If any of this matters to you, the good news is that Kotlin's sealed classes (and soon, Java's sealed classes) allow you to easily implement your own Result-like sum type.

[tsimionescu]

So how did Rust handle the case of a function that may return an error or nothing? Can you forget to check the error, or does it force you to explicitly handle it in some way?

I understand how Result forces you to handle the possibility of an error when you want to access the actual return value, but I don't know what happens if you aren't planning on accessing the return.

I'm also curious how Result-based error handling composes. For example, if I want to sort a list of structs where my comparison function may fail, can I use the built-in sort function, and still get any error that may have occurred back?

With (unchecked) exceptions, this is trivially easy - the sort() function doesn't need to be aware of exceptions in order for them to be propagated through it. With checked exceptions in Java, you need to go through a little dance of wrapping and unwrapping, but it can still be done. If I understand correctly, in Haskell this can be done with the Either monad and liftM, though I can't claim to understand the specifics.

Is there a Rust solution?

[FreeFull]

Rust will also crash if you use the indexing operator and go out of bounds. For arrays, you can also use the .get(index) method which returns an Option<&T> instead of &T, so it doesn't have to crash. For most things, iterators get used instead of indexing anyway.

[wybiral]

> Because it encourages nesting function calls, which is harder for a human to parse than separate statements across lines.

I absolutely agree. Beyond the human parsing aspect it also makes commit changes easier to reason about and review. I want functionality to be limited per-line and view the ability to combine a lot of functionality into one line as a liability more than a benefit.

Go's error handling isn't carefree or hands-off, but that's because error handling is serious. Especially in network code and cryptography.

[gigatexal]

I thought it could lead to doing method chaining for a fluent like API which I find cleaner than how things work now.

[natefinch]

I really dislike method chaining. I'd much rather have 5 lines than 5 chained methods. If that's too much to read, you can always encapsulate it in a well-named function.

[gigatexal]

But five functions that return a value and an error would each have to run the if err != nil dance whereas with method chaining it's cleaner

[NateDad]

not if each one can fail. What if call #1 and call #3 can return the same error.. how does the caller know which one failed? This is the same as wrapping a bunch of calls with a catch (Exception) ... you lose context of what failed and can't behave differently for different failures. All you can do is perform a generic "something went wrong" behavior.

[saturn_vk]

That can easily be done right now with the current way of error handling.

[gigatexal]

Do you have any examples?

[Thaxll]

How returning (val, err) is error prone? It's verbose but it's clear and definitely not error prone. I spent so much time working with Java and useless giant stacktraces or with Python and people not knowing what to do inside a try / except.

[djur]

Repetition and verbosity in a language can create errors in at least two ways. First, by the developer losing track of which error case is which (and/or copy-pasting error-handling logic) and doing the wrong thing in the error case. Second, by reviewers who have become trained to notice and gloss over error-handling boilerplate not noticing when there's something wrong with a particular case.

Concise languages can be more challenging to read because you have to understand more about each symbol/word in the language. But verbose languages can be more challenging to comprehend because there's a lot of symbols which don't signify anything.

[kartickv]

Interesting perspective. Are you expressing an opinion about "explicit is better than implicit", or is your point on a different axis?

I suppose concise / implicit is fine when the thing that's being hidden can't go wrong, like in:

[i * 2 for i in 1...10]

The loop counter increment logic can't possibly go wrong, so it's fine to not think about it.

Regarding error-handling, don't you want to think about? If you're calling a() followed by b(), what should you do if a() fails? In some cases, b() shouldn't be called, but in others, it should, like deleting a temp file. And if you have to think about it, it's better to be explicit?

[djur]

My preferences are that error handling is expressed in and enforced by the type system (Haskell's Maybe/Either, Rust's Result), that common error handling tasks be supported by the standard library and by specialized syntax when necessary (Haskell's many Monad/Applicative tools, Rust's "?" operator), and that if a developer neglects or chooses not to handle an error that the most likely outcome is that it bubbles up to some kind of top-level crash handler that terminates the current task and produces whatever useful diagnostics are possible (exceptions in many languages).

To put it more simply: yes, the developer should have to think about what they do in the case of an error. And then the amount of work they do -- and the code produced, and thus the work reviewers have to do -- should be proportionate to how unusual the necessary error handling is. When I see explicit error handling, that signals to me "hey, this is an important case that we need to handle in a particular way".

[prirun]

the amount of work they do -- and the code produced, and thus the work reviewers have to do -- should be proportionate to how unusual the necessary error handling is.

Great comment. I would add how unusual _and critical_.

One of the things I love about Python is that while I know errors can occur on practically every statement written, I only have to add error handling for likely / expected / critical errors. Any unlikely errors that occur, even in production, will show a detailed stack trace (lots of context), making them easy to fix.

In my experience, things work as expected 98% of the time. For some software, like a pacemaker, checking the execution of every single line of code and even having redundant error checking is not overkill. For other software, like the backup software I work on, having one customer out of 1000 get a weird error is something I'd rather deal with as a support ticket rather than having to anticipate it while writing code.

Of course error handling is important, but requiring 3 lines of error handling for every 1 line of actual code has kept me from investigating Go to replace Python for HashBackup. I'd love to get the performance increase, but not for a 4x expansion of LOC.

[OvermindDL1]

Honestly when I look to rewriting a python thing to be 'faster' either try using PyPy first, or rewrite it in OCaml instead. OCaml is extremely simple, similar to python in a lot of ways (GIL and all), but runs at native code speeds, near C the majority of the work, and super easy to bind to C libraries if you need.

Or try Rust. ^.^

[chc]

Concise and implicit are kind of different axes. For example, Python's "x += 1" is more concise than AppleScript's "set variable x to x + 1.", but the exact behavior of the statement is just as clear from reading it, so it is no less explicit.

In this case, I don't think anyone is arguing that error handling should be implicit. They're saying there should be an explicit way of saying "handle this error in the common way." This actually makes the distinction between common and uncommon cases more explicit, because their differences aren't buried in boilerplate.

[anonymoushn]

You're using defer to close the temp file either way.

[wolco]

you have 'catch' to handle those cases. Try and catch are easy to notice when scanning the codebase.

[kerng]

Copy/paste is very error prone. Golang code is full of it. I see lots of similarities between Visual Basic and Golang, incl. the passionate communities behind the languages.

[mikeschinkel]

Curious, do you see other communities that are not passionate about their languages?

[pjmlp]

With the difference that Visual Basic is an academic language full of needless features from Go's community point of view.

[mikeschinkel]

Visual Basic is hardly academic; they is a tremendous amount of line-of-business code that has been written in VB over the past 25 years.

But yeah, Go dev do not see VB's features as being "features."

[pjmlp]

The point was that many of VB.NET features are what many in the community attack as being academic and not worthy of being adopted by Go.

[mikeschinkel]

Given that I have worked with VB long before .NET even existed, I have a broader view of it than just the more recent criticisms.

VB's biggest problem IMO is that it tried to compete with C# instead of maintaining its original raison d'être which was to be a highly productive tool that required very little programming skill to be able to start building real solutions for business use.

But I digress...

[_hardwaregeek]

It's error prone in that you aren't forced to handle the error. In languages such as Rust or Haskell, you have a Result type which can either be an Ok(val) or an Err(err). In order to "unwrap" a Result, you have to check the error case. Basically there's a compile time guarantee that errors are handled.

[Thaxll]

I'm not a Rust expert but afaik Rust doesn't enforce error checking since you explicitly need to unwrap(). It's very possible to panic because you forgot to check something.

It's similar in Go since you can't compile with unused variable so you need to explicitly discard the error with _. Ex: result, _ := func() This is for multi-value returns, for single value you can even omit the _

https://golang.org/doc/effective_go.html#blank

[jpittis]

Having unwrap() in your Rust code is like littering your code base with panic(). It’s not appropriate to use in most production code, but is convenient in prototypes, examples and tests.

Your example re Go errors is incorrect. The go compiler allows you to ignore errors in returns without any compiler error.

For example

err := doThingThatErrs()

and

doThingThatErrs()

are both valid Go code.

[edflsafoiewq]

There's nothing wrong with unwrap. It's just an assert. Even a[i] is just shorthand for a.get(i).unwrap(). Asserts are definitely appropriate in production code, just not for handling run-time errors.

[jbverschoor]

Then how is this better than anything else? Except for syntactical sugar for:

Try Return [Bla(), null] Catch err Return [null, err] End

I do like this syntax better, bc the different scopes cause a lot of nesting

[Thaxll]

My example is correct I explained all of that, multi values -> need to omit, single value can ignore everything.

[jpittis]

Yup. I misspoke. We’re both right.

[grey-area]

I don't particularly mind try, but would prefer that they addressed the boilerplate which is actually annoying to type out (the convention is to return zero values and the error (annotated or not depending on what other functions have already annotated it)):

if err != nil { return ...,...,err }

If there were a shortcut for returning that error + zero values without interfering with the function call which produces the error (as try does), I'd prefer it. Something more like check(err). We'll see what they come up with next though to try to address this.

I can't say I've ever had problems tracking down an error, not sure what you mean about default values - surely if you check the error you won't use the values returned. My only problem with go error handling is the verbosity, which isn't a huge deal.