Exploring Error Handling Patterns in Go(8thlight.com)
8thlight.com
Exploring Error Handling Patterns in Go
https://8thlight.com/blog/kyle-krull/2018/08/13/exploring-error-handling-patterns-in-go.html
79 comments
In my experience, this just becomes arbitrarily close to "re-implement your stack trace by hand with space-delimited words instead of camelCaseFunctionNamesOrWhatever".
I'll overwhelmingly prefer an always-correct stacktrace over a hand-recreated one that sometimes collapses multiple branches into a single ambiguous on. At least then the devs can help me when it fails. And stack traces and concatenated strings are in no way appropriate error responses for humans unless you're expecting them to be able to navigate the source code, so neither does anything for the "provide a helpful error message for non-programmers" problem.
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this is why stuff like https://github.com/pkg/errors exists. wrap at the deepest level / where the error originates, and it's relatively rare that you need to add context at higher levels. If you want user-friendly errors, you need something dramatically more sophisticated.
I'll overwhelmingly prefer an always-correct stacktrace over a hand-recreated one that sometimes collapses multiple branches into a single ambiguous on. At least then the devs can help me when it fails. And stack traces and concatenated strings are in no way appropriate error responses for humans unless you're expecting them to be able to navigate the source code, so neither does anything for the "provide a helpful error message for non-programmers" problem.
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this is why stuff like https://github.com/pkg/errors exists. wrap at the deepest level / where the error originates, and it's relatively rare that you need to add context at higher levels. If you want user-friendly errors, you need something dramatically more sophisticated.
Just using WithStack() from "github.com/pkg/errors" on any error that originates from outside my repository has been my go-to rule for any Go project. It has never disappointed.
Like an exception?
Except it's just a returned value and not a goto lookalike.
Exceptions—which go straight up the call stack, like returns—are nothing like gotos.
The similarity in both needing to have stack trace does not make them very alike yet. They serve similar purpose and for that purpose the stack trace serves value to the developer.
Returns go straight up the stack only if you choose them to. Caller doesn't have to propagate errors and return immediately, it can hold onto them and/or process them in the natural place they occur, they are just values. The returns from your function can be found with "grep return".
Exceptions, by default, break the natural control flow unless you wrap everything with try/catch. Even then, a lot of constructs won't be very natural and you really will have to get out of your way to identify the source of the exception, which very frequently is more important than it's type.
Returns go straight up the stack only if you choose them to. Caller doesn't have to propagate errors and return immediately, it can hold onto them and/or process them in the natural place they occur, they are just values. The returns from your function can be found with "grep return".
Exceptions, by default, break the natural control flow unless you wrap everything with try/catch. Even then, a lot of constructs won't be very natural and you really will have to get out of your way to identify the source of the exception, which very frequently is more important than it's type.
Why would finding the source of the exception be difficult? The stack trace in exception-based languages goes back to the actual line, as opposed to a stack trace from an error-as-value based language, where it only goes to where you trigger generating the stack trace.
I meant finding it in the context of a coder who writes a function. It's hard to identify which expression and statements can cause exceptions and effectively short-circuit your function. In contrast to explicit errors-returned-as-values.
(Panics of course can cause similar thing in Go but that's the reason why they should rarely be recovered and not used as a value propagation mechanism.)
(Panics of course can cause similar thing in Go but that's the reason why they should rarely be recovered and not used as a value propagation mechanism.)
Is that any worse than the ambiguity in e.g. code like this?
Granted, you could turn this into a compiler error. But it's not currently.
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Anyway. Given that so many not-prevented-by-the-typesystem operations panic, I don't think it's reasonable to assume that any func call will not panic, especially not in the future since they may change. So you already have to program with `defer` to maintain your invariants, which is exactly the same as with exceptions, except you now have to deal with both possibilities for nearly every func.
func thing(arg) {
otherThing(arg) // does this return an error you're ignoring?
}
Granted, you could turn this into a compiler error. But it's not currently.
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Anyway. Given that so many not-prevented-by-the-typesystem operations panic, I don't think it's reasonable to assume that any func call will not panic, especially not in the future since they may change. So you already have to program with `defer` to maintain your invariants, which is exactly the same as with exceptions, except you now have to deal with both possibilities for nearly every func.
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I appreciated the article, but the error handling in Go just bugs me. So verbose...
The built-in tool does not even warn about unused errors... not `go build`, and not `go vet`. What's more important, an ignored error or an unused import?
https://play.golang.org/p/j-oXsZz51ki
The built-in tool does not even warn about unused errors... not `go build`, and not `go vet`. What's more important, an ignored error or an unused import?
https://play.golang.org/p/j-oXsZz51ki
That's by design -- programmer's choice.
I don't understand.
Go errors out on unused imports, but you can type "import _ foo.com/unused-import" to not error out.
Why doesn't 'errors.New("asdf")' error out and require you to instead write '_ = errors.New("asdf")' to ignore the result
I think the real answer is not that it's intentional design, but rather that the original compiler was not powerful enough to implement that feature easily... and once go hit 1., it was impossible for them to add new warnings or errors because there are no warnings and errors are backwards incompatible.
Sure, that means developers use third-party tools for warnings because the go compiler refuses to ever have warnings (that compromises the pure beauty of the language obviously), but at least that means it's only the users that have to deal with the complexity of using more tools, the compiler developers can ignore it.
Go errors out on unused imports, but you can type "import _ foo.com/unused-import" to not error out.
Why doesn't 'errors.New("asdf")' error out and require you to instead write '_ = errors.New("asdf")' to ignore the result
I think the real answer is not that it's intentional design, but rather that the original compiler was not powerful enough to implement that feature easily... and once go hit 1., it was impossible for them to add new warnings or errors because there are no warnings and errors are backwards incompatible.
Sure, that means developers use third-party tools for warnings because the go compiler refuses to ever have warnings (that compromises the pure beauty of the language obviously), but at least that means it's only the users that have to deal with the complexity of using more tools, the compiler developers can ignore it.
I don't think it's because of the complexity. I'm quite sure it would not have been difficult to do.
One of the reason is that you don't always want to check the error. The most common one is fmt.Println.
I would not like to always write
_, _ = fmt.Println("Hello, playground")
One of the reason is that you don't always want to check the error. The most common one is fmt.Println.
I would not like to always write
_, _ = fmt.Println("Hello, playground")
You certainly do not always want to write _,_ = fmt.Println("Hello, playground"), and I think this points out the real lack. What do you want your program to do if fmt.Println starts failing? I think, unless you are explicitly checking for errors, that in all other cases you want it to crash. Rather than silently continue. Which is a bug, and a potentially disastrous one, that is endemic in Go code (and, to be fair, plenty of other languages). Thankfully the practical risk of this particular case is tiny.
This is why you want unchecked errors to implicitly bubble up. Which is what exceptions give you, or perhaps a syntax with implicit error return values rather than Go's by-convention approach.
This is why you want unchecked errors to implicitly bubble up. Which is what exceptions give you, or perhaps a syntax with implicit error return values rather than Go's by-convention approach.
If fmt.Println fails you've likely got bigger problems and the game is over.
And if it means a lot in this case, wrap the function and use it instead.
And if it means a lot in this case, wrap the function and use it instead.
And it’s—bluntly—a terrible design.
Why? I am genuinely curious. Terrible compared to what?
Exceptions.
Anders give an interview in 2003 [1] where he talks about how C# looked to learn from Java's checked exceptions. His conclusion was basically that, in their evaluation, 9/10 exceptions cannot be handled beyond some generic top-level handler.
If this observation is correct, and it certainly aligns perfectly with my own, then bubbling makes a lot more sense.
Note that, with error return values, you can emulate bubbling (which is what most Go programmers end up doing). And with exceptions, you can emulate return values. The question is what's the most common default? And, again, according to Anders, as well as any project I've ever worked on, bubble-by-default is overwhelmingly the most useful thing to support cleanly.
The only way Go's approach makes sense is if you consider it's original goal (system programming) and MAYBE (i don't know, I'm not a system programmer) for such systems you can/need to handle each error. Except that's not really how Go is being used now, so...
[1] https://www.artima.com/intv/handcuffs.html
Anders give an interview in 2003 [1] where he talks about how C# looked to learn from Java's checked exceptions. His conclusion was basically that, in their evaluation, 9/10 exceptions cannot be handled beyond some generic top-level handler.
If this observation is correct, and it certainly aligns perfectly with my own, then bubbling makes a lot more sense.
Note that, with error return values, you can emulate bubbling (which is what most Go programmers end up doing). And with exceptions, you can emulate return values. The question is what's the most common default? And, again, according to Anders, as well as any project I've ever worked on, bubble-by-default is overwhelmingly the most useful thing to support cleanly.
The only way Go's approach makes sense is if you consider it's original goal (system programming) and MAYBE (i don't know, I'm not a system programmer) for such systems you can/need to handle each error. Except that's not really how Go is being used now, so...
[1] https://www.artima.com/intv/handcuffs.html
I've always been annoyed by the parallel control flow introduced by exceptions in any language. They are used so often in many languages where it doesn't feel necessary.
The fact that I don't even have to think if the function call I'm looking at can throw and if I should catch it or not outweighs everything.
The fact that I don't even have to think if the function call I'm looking at can throw and if I should catch it or not outweighs everything.
Easy, just assume it throws. That's the case anyway. Thanks to panics, even in Go.
Edit: Also, there is no parallel control flow. Languages with exceptions have union-type return values, and every statement is implicitly followed by the equivalent of: if err!=nil return nil, err. The fact that in Go you have to type that makes Go cumbersome, not smart.
Edit: Also, there is no parallel control flow. Languages with exceptions have union-type return values, and every statement is implicitly followed by the equivalent of: if err!=nil return nil, err. The fact that in Go you have to type that makes Go cumbersome, not smart.
Not really, in all the years I've been writing Go, only one library used panics for error handling.
Usually if something panics you don't want to handle it. (Other than at the http handler level, where you can just throw an InternalServerError and log the panic)
First and foremost, you can usually assume libraries won't panic, though it would be nice to have a tool (grep) to check for explicit panics.
Usually if something panics you don't want to handle it. (Other than at the http handler level, where you can just throw an InternalServerError and log the panic)
First and foremost, you can usually assume libraries won't panic, though it would be nice to have a tool (grep) to check for explicit panics.
If something "errors", you usually don't want to handle it either. Other that at the http handler level.
Actually, you often do. That's the point really. You should decide if it's an operation you might want to retry, you might also want to just flat out error and do nothing more, maybe you want to provide degraded functionality, like provide some default answer.
I think errors as values cause you to always think about this, which makes you handle errors in a more sensible way, instead of just bubbling up. Sure, 90% of situations you will bubble up, but in my opinion it's still worth it.
I think errors as values cause you to always think about this, which makes you handle errors in a more sensible way, instead of just bubbling up. Sure, 90% of situations you will bubble up, but in my opinion it's still worth it.
You basically said so in your last paragraph, and I agree it's a tradeoff, I just want to reiterate that in my experience, bubbling up and retrying/degrading/failing at the top level (system boundary, client side) makes for a robust (distributed) system you can reason about. Having hundreds of easter eggs in the project where somebody tried to do something smart when encountering an error seems more like a nightmare scenario to me. Old Java enterprise applications are filled with this, and they are rightfully frowned upon. Checked exceptions are the culprit.
I'm not sure I understand the relationship between union-types and exceptions. You mean something like <Result, ErrorData>? Could you expand on that?
> Thanks to panics, even in Go.
Fortunately, for some reason Go developers don't use panic like exceptions and recover them at library boundaries.
> Thanks to panics, even in Go.
Fortunately, for some reason Go developers don't use panic like exceptions and recover them at library boundaries.
<Result, ErrorData>
Yes, exactly like that. In real world programs, every function might fail, even the simplest ones (stack overflow, out of memory, interrupts, etc). No information is gained by declaring a specific function might fail. Also it's almost certainly a lie to declare: this function will never fail. So if every function might fail, why not just produce a union type <Result|ErrorData> for every function return type. Also, lets automatically check for the error case after each nested invocation, and cleanly unwind the stack (returning ErrorData again) on failure. This makes 95% error handling code go away. The ErrorData type uses a special return keyword ("throw"), and in rare cases, errors need to actually be handled, so the union's ErrorData type is exposed to the user code with additional primitives (catch). On all the code in between, the ErrorData type is just hidden behind the scenes.
Yes, exactly like that. In real world programs, every function might fail, even the simplest ones (stack overflow, out of memory, interrupts, etc). No information is gained by declaring a specific function might fail. Also it's almost certainly a lie to declare: this function will never fail. So if every function might fail, why not just produce a union type <Result|ErrorData> for every function return type. Also, lets automatically check for the error case after each nested invocation, and cleanly unwind the stack (returning ErrorData again) on failure. This makes 95% error handling code go away. The ErrorData type uses a special return keyword ("throw"), and in rare cases, errors need to actually be handled, so the union's ErrorData type is exposed to the user code with additional primitives (catch). On all the code in between, the ErrorData type is just hidden behind the scenes.
I actually really like Go error handling (I write Go daily), but truth be said, they're a poor mans Either Monad.
The thing that bugs me is that if you ignore the error (by simply not checking for it), it's still there, possibly insidiously corrupting runtime state. Imagine trying to debug a file format corruption that happened because some obscure part of the code tried to add to the format and instead errored (silently) and added garbage and then the code just kept chugging along until the state REALLY messed things up.
The thing many programmers don't seem to realize is that a program is a model of a design in the programmer's mind. If the model goes off the rails of the expected design/behavior in any way, that should be considered very bad ASAP... or as many languages treat it, "exceptional".
The thing many programmers don't seem to realize is that a program is a model of a design in the programmer's mind. If the model goes off the rails of the expected design/behavior in any way, that should be considered very bad ASAP... or as many languages treat it, "exceptional".
I used to forget to put "set -e" in bash scripts. Then one went off and deleted a whole bunch of important stuff despite a prerequisite command erroring. Now I include it, but remembering one line of code in the header is easy compared to Go's approach of remembering to check every error.
I wish more developers could do "investigation" like this for a new languages they learn.
For me, the main difference between Go's way of handling language and the rest of mainstream languages is that it makes error handling unmagical.
It literally says – errors are just like any other return values. Let's say, if you have function `sqrt` and return a value, and then call this function – you probably is interested in this return value and should handle it somehow (or mute with `_`). Now, the same applies for errors - if function returns the error, you likely to think how to handle it – do something in place or propagate up the stack.
There is also a cultural moment to this. As we mostly learn by examples, and most Go code has proper error checks (not equal to "proper error handling" but nevertheless), it makes newcomers to do the same as well, even while disagreeing with Go's way. I've heard from many devs that Go was the reason that made them appreciate proper error handling.
And honestly, I feel this too, and I think the reason is that in Go it's too easy to "handle errors properly". I never had this feeling with languages with exceptions, where I had to read whole books (!) just to learn how to properly use them and be confident in the way how I handle errors. (this is just an example, not the spark to start return values vs exceptions battle, just in case)
For me, the main difference between Go's way of handling language and the rest of mainstream languages is that it makes error handling unmagical.
It literally says – errors are just like any other return values. Let's say, if you have function `sqrt` and return a value, and then call this function – you probably is interested in this return value and should handle it somehow (or mute with `_`). Now, the same applies for errors - if function returns the error, you likely to think how to handle it – do something in place or propagate up the stack.
There is also a cultural moment to this. As we mostly learn by examples, and most Go code has proper error checks (not equal to "proper error handling" but nevertheless), it makes newcomers to do the same as well, even while disagreeing with Go's way. I've heard from many devs that Go was the reason that made them appreciate proper error handling.
And honestly, I feel this too, and I think the reason is that in Go it's too easy to "handle errors properly". I never had this feeling with languages with exceptions, where I had to read whole books (!) just to learn how to properly use them and be confident in the way how I handle errors. (this is just an example, not the spark to start return values vs exceptions battle, just in case)
The flipside of easy-to-learn is there's no payoff for getting better with the language. Your code will always be exactly as tedious as novices' code because they'd rather conserve compiler cycles than spend them to amplify programmers' work.
On the bright side, your code will always be as easy to understand as a novice's code too, so it conserves other programmer's mental cycles as well.
This is the root of the Go confusion.
The code will indeed still be easily understandable on a line-by-line basis, but larger units (functions, groups of functions, modules) then become harder to read and understand due to large amounts of noise. As you progress along to more advanced, larger codebases, with novice-style code you just pile boilerplate on top of boilerplate.
Larger Go codebases remind me of old versions of Java where they went as far as to embrace all the boilerplate and call it 'design patterns'. It's sad how Go designers recognized that Java code tends to be hard to read and generally bad, but apparently weren't really able to discern why that is. They decided to just blame it all on inheritance and exceptions.
(FTR I'm not advocating for inheritance or exceptions here, but believing that those are the root of Java's problems and simply omitting them will somehow magically make a language better is just naive & shortsighted.)
The code will indeed still be easily understandable on a line-by-line basis, but larger units (functions, groups of functions, modules) then become harder to read and understand due to large amounts of noise. As you progress along to more advanced, larger codebases, with novice-style code you just pile boilerplate on top of boilerplate.
Larger Go codebases remind me of old versions of Java where they went as far as to embrace all the boilerplate and call it 'design patterns'. It's sad how Go designers recognized that Java code tends to be hard to read and generally bad, but apparently weren't really able to discern why that is. They decided to just blame it all on inheritance and exceptions.
(FTR I'm not advocating for inheritance or exceptions here, but believing that those are the root of Java's problems and simply omitting them will somehow magically make a language better is just naive & shortsighted.)
> your code will always be as easy to understand as a novice's code too
Yeah, that seems about perfectly correct. Have you looked at novice's code? Is it easy to understand?
Yeah, that seems about perfectly correct. Have you looked at novice's code? Is it easy to understand?
Yes, we have adopted Go for a lot of things at work and I have reviewed code of many of our devs who are more or less Go novices. It has indeed been pretty easy to understand - much easier than other languages (notably Java in this regard, but Python falls afoul of it a bit too) where people tend to write things in quite different styles and/or with excessive abstraction that made it much harder to understand what was going on.
That's a feature, not a bug. It means I don't have to deal with anyone's 'clever' code.
It's not about saving the compiler work at all, it's about saving the hundreds of humans who have to read your code after you the work of understanding the abstractions you created.
It's not about saving the compiler work at all, it's about saving the hundreds of humans who have to read your code after you the work of understanding the abstractions you created.
Saving the work of understanding abstractions usually means you'll pay the cost of sieving through explicit duplication.
A little duplication is better than the wrong abstraction, and I've seen far more subtly wrong or obfuscating abstractions than duplication in code I have to manage. Go is definitely not perfect, and sometimes it's plain wrong about this (I don't particularly like the go error handling and hope it improves), but there is a reason for discouraging certain types of abstraction and encouraging verbosity and boring code instead, and it's not to save the compiler time.
https://www.sandimetz.com/blog/2016/1/20/the-wrong-abstracti...
https://www.sandimetz.com/blog/2016/1/20/the-wrong-abstracti...
Abstractions like map and filter that have decades of use and countless pages of research behind them are not the wrong abstraction. You are more likely to get the wrong abstraction by forcing programmers to create their own abstractions instead of letting them use well-known ones that have been refined over many years.
I'm not sure anyone was opposed to map (that wasn't under discussion), not all abstractions are bad, however a flexible language makes code easier to write but harder to read, a rigid language makes code harder to write but easier to read. I prefer ones that are easier to read, even at the expense of a little verbosity.
I'm not saying Go is the best of all possible worlds (I would like to see generic functions like map too, or things like sum types for errors), just that there are good reasons for the decision to exclude some opportunities to build abstractions (for example I'm happy go eschews inheritance), and abstraction is not an unmitigated good. I've seen far more bad abstractions built than code duplicated when reading code in any language, so limiting abstractions is not always a bad thing.
I'm not saying Go is the best of all possible worlds (I would like to see generic functions like map too, or things like sum types for errors), just that there are good reasons for the decision to exclude some opportunities to build abstractions (for example I'm happy go eschews inheritance), and abstraction is not an unmitigated good. I've seen far more bad abstractions built than code duplicated when reading code in any language, so limiting abstractions is not always a bad thing.
> A little duplication is better than the wrong abstraction
Besides the notion of "The wrong abstraction", which is sometimes used as a proxy for "Abstractions I don't want to learn", we're discussing about language level abstractions here. The article you quote criticizes user level abstractions.
Language-level abstractions have a decent enough track record that we can assess them. Go even uses some of them: GC is, after all, an abstraction.
There would also be a lot to say about what the "little" in "A little duplication" means.
Besides the notion of "The wrong abstraction", which is sometimes used as a proxy for "Abstractions I don't want to learn", we're discussing about language level abstractions here. The article you quote criticizes user level abstractions.
Language-level abstractions have a decent enough track record that we can assess them. Go even uses some of them: GC is, after all, an abstraction.
There would also be a lot to say about what the "little" in "A little duplication" means.
This. Either you check in a DSL, or you try to compile the DSL to boilerplate in your head and check that in, then everyone has to try to read the boilerplate and try to infer what the DSL would have said.
It's always strange watching programmers defend go's obvious deficiencies. I mean, this sort of "appeal to simplicity" could be used to defend anything.
The reality is most go programs are (1) very difficult to understand because error handling swamps their logic and (2) end up reinventing exceptions anyways, albiet poorly and (3) inevitably end up leaking resources because go's "error handling strategy" doesn't ensure resource cleanup.
We can observe this and measure this quite clearly in non-trivial go codebases.
Eventually the go dictatorship will relent and provide exceptions. At that point all the people who praise the existing broken model will happily praise the new approach and denounce the existing brokenness.
The reality is most go programs are (1) very difficult to understand because error handling swamps their logic and (2) end up reinventing exceptions anyways, albiet poorly and (3) inevitably end up leaking resources because go's "error handling strategy" doesn't ensure resource cleanup.
We can observe this and measure this quite clearly in non-trivial go codebases.
Eventually the go dictatorship will relent and provide exceptions. At that point all the people who praise the existing broken model will happily praise the new approach and denounce the existing brokenness.
I wholeheartedly agree with you. Go got a lot right (concurrency, deployment), but some parts of Go's language design are missing the last two decades of programming language history. To me, arguments supporting Go's error handling approach alway seem a little bit like people are rationalizing a horrible mistake.
That's precisely why Go is loved.
Consistency in reading a code base amplifies work.
"The flipside of easy-to-learn is there's no payoff for getting better with the language. Your code will always be exactly as tedious as novices' code because they'd rather conserve compiler cycles than spend them to amplify programmers' work."
In my years of experience with the language, this is, bluntly, untrue. Go, used properly, is slightly more verbose than most comparable code in Python or Perl. If someone is writing code that is shot through with boilerplate in Go, then I would say that they may be using "Oh, Go just needs lots of boilerplate" as an excuse.
The problem isn't that Go lacks abstraction mechanisms; the problem is that you need to learn how to use the ones that are there and not sit there pining for the ones that are not. I find this to be almost exactly like learning Haskell; you need to learn to use what is there, not sit there pining for what you don't have. Also like Haskell, there are some particular points that it all comes together at once and hurts you, but, then again, there's some places in Go where I've had big wins using the language features too. It does cut both ways. (I've done some fun things with interfaces, and the pervasive io.Reader/Writer support, while not necessarily a feature of the language, can make certain things amazingly easy to do while still retaining incredible flexibility.)
As one example I went through personally, while by the time I learned Go I had a lot of non-OO experience, so I wasn't as stuck on inheritance as someone who only did OO-languages for the last 10 years would be, I still had to adjust to using a generally-OO language (by my standard of the term) that did not support inheritance. It has now been literally plural years since I missed inheritance in Go. (In fact, quite the opposite; I miss easy composition in my other OO languages! Yes, Virginia, it is possible to miss features Go has when using other languages, despite what it may seem like if you only read the criticisms.) But my first couple of months were a bit rougher before I internalized how the composition works and affects the design of your code.
Complaining that Go code is all boilerplate is like someone who tried Haskell but complains that it's just an especially inconvenient imperative language and you end up doing everything in IO anyhow. Nope... you have not yet gotten past your "Writing X in Y" phase. That's fine; there's a ton of languages and platforms and libraries in the world. If you didn't get a short-term payoff from using it, go ahead and move on. But you haven't attained enough mastery to go around slagging on the language/platform/library yet.
(And, again, let me say that, yes, it is somewhat more verbose that Python or something. If you've shrunk your Go down to that level, you probably went too far and are doing something ill-advised. But I find that in practice, for most tasks, it is not that much more verbose. There are exceptions, like heavy duty GUI code or (IMHO) scientific code; the solution is not to use Go for those.)
In my years of experience with the language, this is, bluntly, untrue. Go, used properly, is slightly more verbose than most comparable code in Python or Perl. If someone is writing code that is shot through with boilerplate in Go, then I would say that they may be using "Oh, Go just needs lots of boilerplate" as an excuse.
The problem isn't that Go lacks abstraction mechanisms; the problem is that you need to learn how to use the ones that are there and not sit there pining for the ones that are not. I find this to be almost exactly like learning Haskell; you need to learn to use what is there, not sit there pining for what you don't have. Also like Haskell, there are some particular points that it all comes together at once and hurts you, but, then again, there's some places in Go where I've had big wins using the language features too. It does cut both ways. (I've done some fun things with interfaces, and the pervasive io.Reader/Writer support, while not necessarily a feature of the language, can make certain things amazingly easy to do while still retaining incredible flexibility.)
As one example I went through personally, while by the time I learned Go I had a lot of non-OO experience, so I wasn't as stuck on inheritance as someone who only did OO-languages for the last 10 years would be, I still had to adjust to using a generally-OO language (by my standard of the term) that did not support inheritance. It has now been literally plural years since I missed inheritance in Go. (In fact, quite the opposite; I miss easy composition in my other OO languages! Yes, Virginia, it is possible to miss features Go has when using other languages, despite what it may seem like if you only read the criticisms.) But my first couple of months were a bit rougher before I internalized how the composition works and affects the design of your code.
Complaining that Go code is all boilerplate is like someone who tried Haskell but complains that it's just an especially inconvenient imperative language and you end up doing everything in IO anyhow. Nope... you have not yet gotten past your "Writing X in Y" phase. That's fine; there's a ton of languages and platforms and libraries in the world. If you didn't get a short-term payoff from using it, go ahead and move on. But you haven't attained enough mastery to go around slagging on the language/platform/library yet.
(And, again, let me say that, yes, it is somewhat more verbose that Python or something. If you've shrunk your Go down to that level, you probably went too far and are doing something ill-advised. But I find that in practice, for most tasks, it is not that much more verbose. There are exceptions, like heavy duty GUI code or (IMHO) scientific code; the solution is not to use Go for those.)
> I've heard from many devs that Go was the reason that made them appreciate proper error handling.
I agree that in some way, this is actually a good reason to support Go's tedious way of handling errors.
Yet, it's akin to avoiding functions (because stackframes are magical), or "for" loops (because their condition block is magical), or threads (because: magic). There is only so much a non-toy programming language should compromise in order to accomodate beginners. People may draw different lines here, but Exceptions (in garbage collected languages) are so completely unmagical, that the line should definitely not be drawn here. In fact, they do exactly what return nil, err does, thousands of times, over and over. In Go you can enjoy writing that code yourself. Also, Go's language designers accepted defeat when they had to add panics. I bet that beginners now just make the mistake of ignoring them instead.
I agree that in some way, this is actually a good reason to support Go's tedious way of handling errors.
Yet, it's akin to avoiding functions (because stackframes are magical), or "for" loops (because their condition block is magical), or threads (because: magic). There is only so much a non-toy programming language should compromise in order to accomodate beginners. People may draw different lines here, but Exceptions (in garbage collected languages) are so completely unmagical, that the line should definitely not be drawn here. In fact, they do exactly what return nil, err does, thousands of times, over and over. In Go you can enjoy writing that code yourself. Also, Go's language designers accepted defeat when they had to add panics. I bet that beginners now just make the mistake of ignoring them instead.
My first (real world) exposure to exceptions was Python. I was a bit above novice. I would write some code, run it, and it would die of some horrible exception. I would catch that exception, try again, and die again. Lather, rinse, repeat. Eventually I would wrap everything in try-except blocks. Talk about verbose; tab indents everywhere. You can often end up handling exceptions somewhere not immediately close to the call that failed.
I liked when I started with Go (mostly due to concurrency primatives, but errors were nice too). In my day job, many of the errors have a need for custom handling and I get that for "free" in Go and I am never surprised by a program crash because I failed to read the docs on a function and what exceptions it may throw (or undocumented exceptions it may throw due to one of its dependencies). I can see right in the signature that I have an error to potentially handle.
I liked when I started with Go (mostly due to concurrency primatives, but errors were nice too). In my day job, many of the errors have a need for custom handling and I get that for "free" in Go and I am never surprised by a program crash because I failed to read the docs on a function and what exceptions it may throw (or undocumented exceptions it may throw due to one of its dependencies). I can see right in the signature that I have an error to potentially handle.
Maybe you would like the concept of "checked exceptions" from Java? Exceptions are part of a method signature and not handling them is a compiler error, but they're still exceptions, not return values.
What is not covered here, and what I'm still searching for a good pattern for, is being able to return different errors depending on the type of failure.
Suppose you have a function that fetches a model from your database. It can return an error if the given user doesn't have permission to fetch this model, or it can return an error if your db connection barfs for some reason. The calling function needs to be able to differentiate between the two errors. Most of what I've read on the subject makes it seem like people prefer to only ever check if err != nil.
The two options I've seen in the wild are:
1. Create a constant for a given error, like:
Suppose you have a function that fetches a model from your database. It can return an error if the given user doesn't have permission to fetch this model, or it can return an error if your db connection barfs for some reason. The calling function needs to be able to differentiate between the two errors. Most of what I've read on the subject makes it seem like people prefer to only ever check if err != nil.
The two options I've seen in the wild are:
1. Create a constant for a given error, like:
var ErrFetchForbidden = errors.New("FETCH_FORBIDDEN")
if err == ErrFetchForbidden {
return 403
} else if err == ErrFetchNotFound {
return 404
} else {
return 500
}
type ErrFetchForbidden string
var err ErrFetchForbidden = "error retrieving the user object"
return err
switch v := err.(type) {
case ErrFetchForbidden:
return 403
case ErrFetchNotFound:
return 404
default:
return 500
}
There's another one I often use:
Create a custom error type, for example DB Error:
Otherwise, you can use 2# with a twist, instead of matching on a type, you can do:
Create a custom error type, for example DB Error:
type DBError struct {
Temporary bool
NetworkBased bool
Cause error
}
Otherwise, you can use 2# with a twist, instead of matching on a type, you can do:
switch {
case isErrFetchForbidden(err):
case isErrFetchNotFound(err):
}
IsBadRequest(err)
IsInternal(err)
IsTimeout(err)So you then define your function to return the type DBError instead of a generic err type. That makes sense to me but for some reason some of the stuff I've suggests that just returning err is more go-like.
> The other bit of good news is that you can't unknowingly ignore a returned error, like you can with an unchecked exception. The compiler will force you at a minimum to declare the error as _, and tools like errcheck do a good job of keeping you honest.
Actually, we unknowingly ignore returned errors much more often than we think, like when we call a function and opt out of assigning any of the return values to variables. Consider this function, which returns a single value (being an error).
Actually, we unknowingly ignore returned errors much more often than we think, like when we call a function and opt out of assigning any of the return values to variables. Consider this function, which returns a single value (being an error).
func Failure() error {...}
Failure()
writer.Write([]byte("Hello")) // returns (n int, err error)
errcheck is a good tool to help with this.
For everybody who is interested in improving his error handling skills:
https://dave.cheney.net/2016/04/27/dont-just-check-errors-ha...
https://dave.cheney.net/2016/04/27/dont-just-check-errors-ha...
if err != nil
return err
if err != nil return err
if err != nil return err
https://github.com/docker/cli/search?q=%22if+err+%21%3D+nil%...
https://github.com/kubernetes/kubernetes/search?q=%22if+err+...
https://github.com/coreos/etcd/search?q=%22return+err%22&uns...
https://github.com/influxdata/influxdb/search?q=%22if+err+%2...
The reality of Go's error handling is that you just implement exactly what exception bubbling does painfully by hand.
if err != nil return err
if err != nil return err
https://github.com/docker/cli/search?q=%22if+err+%21%3D+nil%...
https://github.com/kubernetes/kubernetes/search?q=%22if+err+...
https://github.com/coreos/etcd/search?q=%22return+err%22&uns...
https://github.com/influxdata/influxdb/search?q=%22if+err+%2...
The reality of Go's error handling is that you just implement exactly what exception bubbling does painfully by hand.
This is not correct. Exceptions do different things than report an error. They unwind the stack. That's why they are called exceptions and not errors.
One important benefit of Go's error handling pattern is readability. With exceptions, it's not easy to see who handles it and where. There is indeed less code, and that's nice for the writer, but from the reader perspective, error handling becomes obscure. And from the quality control point if view, this becomes unsafe.
One important benefit of Go's error handling pattern is readability. With exceptions, it's not easy to see who handles it and where. There is indeed less code, and that's nice for the writer, but from the reader perspective, error handling becomes obscure. And from the quality control point if view, this becomes unsafe.
The parent is correct. Returns also unwind the stack.
> One important benefit of Go's error handling pattern is readability
I beg to differ, Go's approach is similar to checked exceptions, Java's original sin. And just like checked exceptions, forcing the invoker of a function to handle the error directly is the wrong approach in the vast majority of cases. It just produces code noise and catch/wrap/throw style code, commonly found in old Java enterprise projects. This obsfucates the default path and makes middleware very hard to write.
> With exceptions, it's not easy to see who handles it and where.
Making errors part of the function signature encourages developers to handle them directly at the call site. Which is where most buggy and unreliable error handling is found. The default approach of safely unwinding the stack until you reach the http handler (or equivalent), returning 500 applies to error codes as well. It should be simple to do, automatic even, so novice programmers write robust code out of the box. Hence exceptions.
> One important benefit of Go's error handling pattern is readability
I beg to differ, Go's approach is similar to checked exceptions, Java's original sin. And just like checked exceptions, forcing the invoker of a function to handle the error directly is the wrong approach in the vast majority of cases. It just produces code noise and catch/wrap/throw style code, commonly found in old Java enterprise projects. This obsfucates the default path and makes middleware very hard to write.
> With exceptions, it's not easy to see who handles it and where.
Making errors part of the function signature encourages developers to handle them directly at the call site. Which is where most buggy and unreliable error handling is found. The default approach of safely unwinding the stack until you reach the http handler (or equivalent), returning 500 applies to error codes as well. It should be simple to do, automatic even, so novice programmers write robust code out of the box. Hence exceptions.
Seriously, exceptions are very different from returning an error. Confusing error return with checked exception tells it all. A checked exception is just an exception type specification.
When you read code with a call to a function returning an error, you see how the error is handled. With exception, unless there is a try/catch close surrounding the call, you don't know where and how an exception is handled.
To me, throwing exceptions is like littering the streets. That feels fine for the one who does it, because he assume someone else will take care of the mess. But the problem is taking care of it, who, how when ? With big projects, this strategy is unmanageable.
Correctly handled exceptions don't make middle-ware easier to write or more readable. On the contrary.
You know that programs are not only http handlers, right ?
When you read code with a call to a function returning an error, you see how the error is handled. With exception, unless there is a try/catch close surrounding the call, you don't know where and how an exception is handled.
To me, throwing exceptions is like littering the streets. That feels fine for the one who does it, because he assume someone else will take care of the mess. But the problem is taking care of it, who, how when ? With big projects, this strategy is unmanageable.
Correctly handled exceptions don't make middle-ware easier to write or more readable. On the contrary.
You know that programs are not only http handlers, right ?
> A checked exception is just an exception type specification.
A checked exception _requires_ an exception type specification. If you don't handle the exception locally, that is. It's this quality I refer to, when I say checked exceptions are similar to error codes: an API designer, without knowing the full context, requires the call site to do something about it, even if 9/10 call sites could not care less, _especially_ in big projects. Some other commenter linked to this interview [0], which elaborates on that problem.
> With big projects, this strategy is unmanageable.
Clearly, it's possible to have mantainable projects both with and without exception handling.
> You know that programs are not only http handlers, right ?
I find this somewhat condescending, but yes, I do know that. Most programs have system boundaries though, and might recover from quite severe error conditions there.
[0] https://www.artima.com/intv/handcuffs.html
A checked exception _requires_ an exception type specification. If you don't handle the exception locally, that is. It's this quality I refer to, when I say checked exceptions are similar to error codes: an API designer, without knowing the full context, requires the call site to do something about it, even if 9/10 call sites could not care less, _especially_ in big projects. Some other commenter linked to this interview [0], which elaborates on that problem.
> With big projects, this strategy is unmanageable.
Clearly, it's possible to have mantainable projects both with and without exception handling.
> You know that programs are not only http handlers, right ?
I find this somewhat condescending, but yes, I do know that. Most programs have system boundaries though, and might recover from quite severe error conditions there.
[0] https://www.artima.com/intv/handcuffs.html
> […] function returning an error, you see how the error is handled.
In practice you only see that errors get returned immediately. Most functions rightly give up rather than trying to handle errors because they don't know exactly how or where they're being (re)used.
In practice you only see that errors get returned immediately. Most functions rightly give up rather than trying to handle errors because they don't know exactly how or where they're being (re)used.
Let's imagine a syntax-sugared Go...
Every function has a hidden "err" return value
Every function has an "exceptionExit:" block, by default it does just "return err;"
After every function call, an automatic "if err != nil {goto exceptionExit}" is added.
You can add an "exception" block to a function, it replaces the default.
Now you have function level exceptions in Go just by syntax sugar, without stack unwinding and without requiring new compiler functionality, just syntax sugar.
Every function has a hidden "err" return value
Every function has an "exceptionExit:" block, by default it does just "return err;"
After every function call, an automatic "if err != nil {goto exceptionExit}" is added.
You can add an "exception" block to a function, it replaces the default.
Now you have function level exceptions in Go just by syntax sugar, without stack unwinding and without requiring new compiler functionality, just syntax sugar.
> They unwind the stack.
That's my point. returning the err until some caller above you handles it is unwinding the stack. You're just forced to do it manually at every single level of the stack.
That's my point. returning the err until some caller above you handles it is unwinding the stack. You're just forced to do it manually at every single level of the stack.
> One important benefit of Go's error handling pattern is readability.
Maybe; personally I find it increased clutter that obscures readability (much as do checked exceptions.)
> With exceptions, it's not easy to see who handles it and where.
Who handles it and where is the one thing that is explicit and readily apparent with unchecked exceptions. What can be harder to see with unchecked exceptions than with error returns or checked exceptions is who (other than the original source) throws it and requires consideration of handling it or ignoring/rethrowing it in the caller.
Maybe; personally I find it increased clutter that obscures readability (much as do checked exceptions.)
> With exceptions, it's not easy to see who handles it and where.
Who handles it and where is the one thing that is explicit and readily apparent with unchecked exceptions. What can be harder to see with unchecked exceptions than with error returns or checked exceptions is who (other than the original source) throws it and requires consideration of handling it or ignoring/rethrowing it in the caller.
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At the cost of making the entire logic's readability less which to me is more important than sometimes getting confused where errors bubble up to.
The philosophy is different when, for example the author of Ruby wanted to make coding fun for programmers and does a good job at it and Go is sticking to 'this must be right' approach and breaks some people's heart.
Personally I'd appreciate being more 'fun'.
The philosophy is different when, for example the author of Ruby wanted to make coding fun for programmers and does a good job at it and Go is sticking to 'this must be right' approach and breaks some people's heart.
Personally I'd appreciate being more 'fun'.
I used ruby for a long time and Go more recently. I think Go is fun. I’m able to read code bases with consistency. In a lot of Ruby apps, I see creative flexing that is unique to that person, or teams style.
The fun part is getting code written, and shipped. And it stays fun when it’s maintainable and production ready.
I’m having a lot of fun shipping Go code. :) I definitely can understand a codebase a lot faster than a random ruby one. That may be a personal thing but it works for me.
The fun part is getting code written, and shipped. And it stays fun when it’s maintainable and production ready.
I’m having a lot of fun shipping Go code. :) I definitely can understand a codebase a lot faster than a random ruby one. That may be a personal thing but it works for me.
Depends on your definition of fun, I guess. I personally don't like Ruby because of that fun-factor. In most cases, it makes programming easier for the novice, but more complicated for the experienced.
This is because to make it easier for the novice, there are all kinds of constructs that try to make the code imitate normal English. But coding software is a completely different thing than writing text, thus the English-like front is in fact a smoke screen that hides the real gears.
A small example would be the unless keyword. It completely throws me of each time I come across it, because it reverses the order of evaluation:
Do something, unless condition applies.
I read that from left to right, so in my mind "Do something" has already executed, but then I have to go back, because the condition might not apply. This get really 'fun' if the condition is something negative.
I like Go just because it way more simple. Even it is a bit more verbose in the error handling, everywhere else it is very minimal and clear.
This is because to make it easier for the novice, there are all kinds of constructs that try to make the code imitate normal English. But coding software is a completely different thing than writing text, thus the English-like front is in fact a smoke screen that hides the real gears.
A small example would be the unless keyword. It completely throws me of each time I come across it, because it reverses the order of evaluation:
Do something, unless condition applies.
I read that from left to right, so in my mind "Do something" has already executed, but then I have to go back, because the condition might not apply. This get really 'fun' if the condition is something negative.
I like Go just because it way more simple. Even it is a bit more verbose in the error handling, everywhere else it is very minimal and clear.
That's only the postfix version of unless though, and you could use if the same way. And inversely, you can use unless is its own block, like if.
Error/Either monads are the perfect middle ground IMHO. You get errors as data types and an efficient way to abstract away the boilerplate associated with it.
Yes, I quite liked this about Rust's `Result` and `Option` type and using monads in general but I don't think Golang could achieve this pragmatically without generics.
The pattern is the programmer's choice. Here's a contrary example/approach:
https://blog.golang.org/errors-are-values
https://blog.golang.org/errors-are-values
Claiming "errors are values" is as useless as claiming anything in computing is "a value" (because it is).
Errors are not just values, however, they're something much more specific: An uncaught error is a specific circumstance where the programmer's mental model was insufficient to account for all the state possibilities. Literally the introduction of the unexpected. And this should be treated as a very bad (or at least a very special) thing, as soon as possible. Hence, runtime exceptions. (Hence, disclaimer alert, I'm not a fan of Go.)
Errors are not just values, however, they're something much more specific: An uncaught error is a specific circumstance where the programmer's mental model was insufficient to account for all the state possibilities. Literally the introduction of the unexpected. And this should be treated as a very bad (or at least a very special) thing, as soon as possible. Hence, runtime exceptions. (Hence, disclaimer alert, I'm not a fan of Go.)
The first time I used Go on a big project, error handling bugged me enough that I wrote a package that let me use errors like exceptions:
https://github.com/s4y/go-exc
I’m not sure if I’d use it again today, but it was a fun exercise.
https://github.com/s4y/go-exc
I’m not sure if I’d use it again today, but it was a fun exercise.
Errors should be "decorated" (wrapped, contextualized...) in 99% of the cases.
In the end you get errors that describe step by step what your program tried to do and why it failed, for example:
* could not load profile: could not open file: permission denied.
* could not download profile image: could not open URL: HTTP GET failed: network is down.
This has many advantages:
1. Much more readable than stack traces (especially if they include source file and line information or exception class names: users don't care about those.)
2. Errors are still easy to grep in code to work out the program flow (the stack trace, basically.)
3. When reading the code, you can see from the error context strings what the code is actually doing. Basically it serves a function of comments and (unlike comments) error strings remain up to date.
It is definitely verbose, especially the not equal nil part, as it's a result of Go attempt not to have special cases. Also it's a pity that errors can be silently ignored: maybe Go2 could be stricter here.
Overall, I think this is one of the best approaches at error handling.