Proposal: A built-in Go error check function, try

Go error handling is not like that. But I can sure as hell say fairly that Go error handling is likely also not similar to what you did for 20 years in the 80s and 90s either. Rob Pike and friends surely knew a lot about what programming was like at that time. I, being relatively a youngster, don’t first hand, but I can tell you my experiences with C++, PHP, Python have not been nearly as good as Go with error handling.

For one thing, C++ has no rigid standard for how to handle errors. Some people use exceptions, some used error methods on classes (including the standard library,) some used special integer or enumeration values (...including the standard library,) and some had libraries and frameworks have their own magic error handling mechanisms. This cognitive overhead was horrible. C wasn’t much better; atoi is a case study in why error handling in C sucks. Libraries that tried to standardize it, like SDL, were bearable if it was all you used, but it probably wasn’t, and some APIs, like Win32, made it even worse. (And I suppose it is worth at least mentioning setjmp/longjmp error handling. I don’t think it’s necessary to comment on why it’s not good.)

Python exception handling is admittedly better, but its not really wonderful. Exception handling code in Python is prone to breakage that is first detected at runtime. If a function implementation changes, and the set of exceptions it might throw changes, that’s an invisible API change that may cause an unhandled exception in production. Not so great. Also, on a vaguely related note, you can’t really do error values using multiple returns like in Go, because Python doesn’t support multiple returns, only tuples, and refactoring between returning values and tuples is likely to run into accidental runtime errors (though you can paper over this issue a bit with type checking.)

PHP error handling sucks, I will withhold from elaborating.

All of the exception handling mechanisms suffer from one problem I really don’t like: it’s another nearly invisible part of the API. It makes the wrong thing (not handling errors) easy, and the right things (handling the appropriate errors correctly) hard. Your dependencies have to care about your call tree, and if it changes in refactoring it’s anyones bet what kinds of exceptions your function might throw. You could catch all exceptions, but because language errors like syntax errors (JavaScript) and index out of range and property name errors (Python) can also be exceptions, you rarely want to catch all exceptions. Not to mention, your call itself would be caught, so any exceptions caused by anything else in the try block would also be conflated.

Go does some things that are mostly not new, but haven’t all been packaged together this way before exactly:

- Custom errors via implicit interfaces, allowing easy, arbitrary data to be passed through errors while maintaining full control of error messages

- Deep separation of programming errors and operational errors tend to be passed as error values. Programming errors, like indices being out of bound or misusing an API, typically results in a panic, whereas operational errors. Very seldom do you actually care what the error is, but when you do you can inspect the error as any other value, because it is just any other value.

- Ecosystem-wide standards for how to pass errors. It’s almost 100% universal that errors are passed at the end of the return list. This makes it easy to parse for humans and easy to lint for machines. Linters can warn you about unused error values, and if a function suddenly has an error return it’s an API break, forcing you to fix existing code to properly handle errors.

- Good library support for error types, including fmt.Errorf for one-off errors that don’t need special handling, and (third party) a myriad of error wrapping/helper libraries. They’re not needed at all, but can be quite handy.

It works a lot better imo. You have more ceremony but less guessing. You can read a function and see almost every edge case, and when all of the functions perform good error hygiene you no longer need to guess about what refactoring your code will do.

I’ll take my repetition.

See, I get the exact opposite tendency. Exceptions mean that any statement, no matter how seemingly trivial from the caller's perspective, can fail. It means I'm constantly thinking "If an exception is thrown between X() and Y(), does it break any assumptions I've made about the program state?". You end up with hacks like putting code in finally blocks just to prevent partial execution.

I think exceptions would work fine in a language that also had built-in support for transactional memory, where you could commit or rollback operations when an exception is thrown partway through. Without any language support, though, I think that exceptions and mutable state do not play nicely with one another.

In rust that's fine because the type system will document what error types can be returned.

In golang, it important that every error type that can be returned is manually documented. Otherwise, it's better to just panic, since nobody can handle unknown errors anyways..

Or am I missing something?