foo ? { bar }
Maybe it's just because I originally come from C, where `foo ? bar : baz` meant "if foo then bar else baz", but the fact remains...
func mayfail() error {
if snafu {
return errors.New("oops")
} else { return nil}
}
err := mayfail()
if err != nil { handle }
foo else { bar } { foo } catch { bar }foo ?! { bar }
But, now we’re potentially confusing the “negation” and the “exclamation” meanings the bang symbol usually tries to communicate.
foo ?? { bar }
foo ?/ { bar }
foo ?: { bar }
foo ?> { bar }
foo ||> { bar }
Im not sure I like the idea at all though. It seems like a hack around a pretty explicit design choice. Although I do tend to agree the error handling boilerplate is kind of annoying.
foo or { bar }Once you've been using the language for awhile, you begin to dislike the elaborate system of rugs other languages have to sweep errors under. Errors in Go are right there, in your face, and undeniable that the operation you are doing can be faulty somehow. With good error wrapping, you can trace down exactly which of these `if err != nil` blocks generated the error without a stack trace. If it bothers you that much, you can always make a snippet / macro for it in your editor.
I find it bizzare that go so strongly relies on this pattern, but lacks the features to make sure you actually check for errors.
The pattern we're talking about is returning errors and having to explicitly check for them, right? How does the lack of "algebraic data types/enum/unions" make this pattern un-ergonomic?
This implies that the only people who dislike Go's error handling are newbies that "don't get it".
Go's error handling is objectively bad for two reasons:
1. You are never forced to check or handle errors. It's easy to accidentally miss an `if err != nil` check, I've seen sages and newbies alike make this mistake.
> Errors in Go are right there, in your face, and undeniable that the operation you are doing can be faulty somehow.
2. Repeating `if err != nil` ad nauseam is not handling errors. Knowing the operation can be faulty somehow is a good way of putting it, because in most cases it's difficult — if not impossible — to figure out what specific failures may occur. This is exacerbated by the historical reliance on strings. e.g., Is it a simple issue that can be easily recovered? Is it a fatal error?
While I also don't like Go's error handling approach I thought Go compiler gives an error if a variable is unused, in this case `err`. Is this not the case?
There are linters that do, and I am of the opinion they should be added to `go vet`.
> Knowing the operation can be faulty somehow is a good way of putting it, because in most cases it's difficult — if not impossible
Guru was once able to tell you exactly what errors could be generated from any given err. Now that the world is LSP, we have lost this superpower.
``` if (foo.bar?.baz?.[5]?.bazinga?.value) ```
Is so much nicer than
``` if foo.bar and foo.bar.baz and foo.bar.baz[5] and foo.bar.baz[5].bazinga and foo.bar.baz[5].bazinga.value ```
I honestly don't care which one of those is falsy, my logic is the same either way.
This enables you to ergonomically pass around meaningful domain-oriented objects, which is nice.
Edit: looks like optional chaining is a separate proposal – https://github.com/golang/go/issues/42847
Its funny because when I was a beginner in both I strongly preferred python syntax. I thought it was much simpler.
if dict.get('key', {}).get('key-nested',{}).get....:I tend to use logs with line numbers to point to where errors occur (but that only gets me so far if I’m returning the error from a child function in the call stack.)
We've converted a few scripts and webapps from Python to Go, and if one does default handling ("return err") the error logs became significantly less useful, compared to exception backtraces. Yes, there are ways around it, but most tutorials don't show them.
But go's do not have to be. A compiler can expand "foo()?" to something like:
err := foo(); if err != nil { return err.WithStringContext("foo() in MyFile.go:25"); }
The only complexity there is appending a constant pointer to "err", and this only happens in error case that uses "?". Depending on implementation it could be a single word write, if compiler can prove there are no other users of "err".
(And if your code is carefully written to be allocation-free and appending a pointer kills that? In this case, you don't have to use "?", put "return err" directly.)
Go error handling should remain simple, like the language.
These are all tools, just pick the one you like and stop trying to make them like others.
I'm not so sure I agree with that. I'm glad Rust continues to evolve at a healthy pace and pick up new syntactic features.
Boilerplate is a sin against the brain. As long as you don't pay it down with increased cognitive complexity, it should be eliminated at all costs.
Error handling is such an essential feature of problem solving that this should be one of the highest priorities for a language to get right. It should be so simple and elegant that you can bash it out in a few tokens, and almost impossible to get wrong.
I think Go would be a much better language if it took this to task. I reach for Rust for out of domain problems because it's so expressive and intentional and safe and concise.
I find this a bit odd. Isn't the idea of the primitive error handling that it is obvious and easy, as in "functions can return multiple results, a popular pattern is to return the good result and the error as two separate nullable values of which exactly one will be not null, so you can check if err == nil."?
If you go with fancy error handling anyway, how is this '?' better than returning a Result and do something like foo().getOr { return fmt.Errorf("Tja: %v", err) }
It's clearer because when you see ? you know it's returning the error in the standard way, and it can't be some subtly different variation (like checking err, but returning err2 or a non-nil ok value). The code around it also becomes clearer, because you can see the happy path that isn't chopped up by error branches, so you get high signal to noise ratio, fewer variables in the scope, without losing the error handling.
1. The language has the feature of returning multiple values, which is then used in an error handling pattern.
2. The proposal is about special syntax for that pattern
3. Languages that have generics (like Go) can instead implement a Result type, turning this pattern into more readable code without the extra syntax.
I feel like a Result type would have more advantages and be less disruptive than a syntax macro for a pattern, but I'm not sure.
He submitted, what, 8 failed generics proposals before Phil Wadler came in to figure out what he was missing?
I don't mean to diminish what he has done. He is clearly an important contributor and even those failed proposals were important steps along the way. What I do mean is that judging a proposal based on who it is written by is silly. Imagine if one of those early generics proposals were taken seriously just because of who he is. I expect even he would be unhappy about that outcome in hindsight.
The author is irrelevant. If it is a good proposal, it can stand on its own merits.
Criticism:
> Within the block a new variable err is implicitly declared, possibly shadowing other variables named err
Shadowing here is strange, and I would prefer a design where it did not shadow other variables named err, but rather threw a compiler error concerning the re-declaration of a variable. That would effectively mean that you can't mix-and-match this syntax with old error-handling inside one function, because code like this would fail to compile:
func Test() {
user, err := GetUser("12345")
if err != nil {
panic(err)
}
EmailUser(user) ? {
panic(err)
}
}
I'm not going to invoke the slippery slope argument, but what distinguishes Go from the pack is how explicit it is. It can make it more tedious to write, but also much easier to follow as a reader.
"The goal of this proposal is to introduce a new syntax that reduces the amount of code required to check errors in the normal case, without obscuring flow of control."
The key is "check errors in the normal case".
When the core principles of Go have always been simplicity, flexibility, and having one way of doing things, this feels completely like a step in the opposite direction. We will have syntax sugar for "normal cases" while still relying on the `if err != nil` block for everything else. It’s similar to how we now have both `iterators` and `for loops` as constructions for loops.
> Disadvantage 4: No other block in Go is optional. The semicolon insertion rule, and the fact that a block is permitted where a statement is permitted, means that inserting or removing a newline can convert one valid Go program into another. As far as I know, that is not true today.
Yeah, this seems like a big problem to me, personally. Go has a fair number of lingering foot guns but this is one too far IMO. I think the no-block case should require something else to follow it, perhaps the return keyword. That'd also help prevent it from being as easily missed...
But my biggest beef is the implicit variable declaration, I can’t stand it. That’s just lazy, bad design.
That’s not a great proposal overall, and I suspect if the same proposal had been made by someone else outside of the Go core team, we would have not heard of it.
I hope it gets rejected.
In my opinion everything should return type like MayFail<T>, Result<T>
The proposal is nice, but a bit shallow.
The convention is that error should be the last return value. If the error is not nil, then discard other returned values.
To demonstrate my tweak to your idea, imagine this example code:
r, err := SomeFunction() if err != nil { return fmt.Errorf("something 1 failed: %v", err) }
r2, err := SomeFunction2() if err != nil { return fmt.Errorf("something 2 failed: %v", err) }
r3, err := SomeFunction3() if err != nil { return fmt.Errorf("something 3 failed: %v", err) }
In the current proposal it would turn into this:
r := SomeFunction() ? { return fmt.Errorf("something 1 failed: %v", err) }
r2 := SomeFunction2() ? { return fmt.Errorf("something 2 failed: %v", err) }
r3 := SomeFunction3() ? { return fmt.Errorf("something 3 failed: %v", err) }
My first suggestion is to keep `err` variables visible. It ends up being not much longer, but it is much more readable and Go-like:
r, err := SomeFunction() ? { return fmt.Errorf("something 1 failed: %v", err) }
r2, err := SomeFunction2() ? { return fmt.Errorf("something 2 failed: %v", err) }
r3, err := SomeFunction3() ? { return fmt.Errorf("something 3 failed: %v", err) }
My second suggestion is to require ? to always have a block, and also allow them to "chain" so only the last statement needs a block:
r, err := SomeFunction() ? r2, err := SomeFunction2() ? r3, err := SomeFunction3() ? { return fmt.Errorf("something 1, 2 or 3 failed: %v", err) }
As you can see this is much shorter! Having the block is always required at the end of the "chain" of question mark statements is more consistent with how `if` statements require a block currently. It also makes the `return err` flow also always visible (no return magic). It also also has a huge advantage of it being much harder to miss a question mark syntactically. as a question mark without a block would be a syntax error.
For example, this is an error:
r, err := SomeFunction() ? // <-- compile error: missing block after ?
And also this is an error:
r, err := SomeFunction() ? r2, err := SomeFunction2() // <-- compile error: missing block after ? r3, err := SomeFunction3() ? { return fmt.Errorf("something 1, 2 or 3 failed: %v", err) }
Thanks for listening! Curious what folks think.
But now we have LLM copilots, so writing boilerplate in any language is dramatically more optional.
And I don't see this proposal significantly improving readability of the code.