This isn’t true. Go has a basic standard package list. https://pkg.go.dev/std
#[derive(Hash)] struct X{ ... }
Seems easy enough to me? The only annoyance is if a third party type didn't implement Hash, but you can solve that with a manual implementation instead of a derive.
How? I thought the orphan rule said you can only define trait implantations at struct definition or trait definition
In crystal there is a reasonable data-based default hash implementation that you can just rely on.
What, apart from string reverse, do you miss for real projects?
First, it has a lot of useless packages you typically wouldn't use, like "log" and "flag" (which work, but are way worse than third party alternatives like logrus and pflag), but also like "syscall" (as it says 'deprecated, use 'golang.org/x/sys' instead), "image/draw" (nope, you wanted 'golang.org/x/image/draw' usually), "path" for working with paths (you wanted "filepath"), "net/rpc" and "rpc/jsonrpc", "plugin" (almost always a bad idea), a chunk of "strings" (use "golang.org/x/text" for proper unicode support) and so on. Some of those are marked deprecated, most of them are not, and are just waiting for someone to accidentally use them.
That's issues I have with the stdlib and not stuff I'm missing though... Though I guess I really do miss a good logging library, or at least interface for external packages to implement so I can plug in logging libraries without rewriting the world.
One thing I do find missing frequently is a reasonable set type with the ability to do things like basic set operations (intersect, diff, etc). I constantly have to write ad-hoc for loops in go to do set operations, and it's verbose, non-obvious what the code does, and easy to get wrong.
But honestly, the main thing I'm missing isn't actually a package, but more about error handling for the stdlib as a whole, which is more a language issue. I really wish I could know what possible errors stdlib functions returned without, fairly often, having to read huge chunks of stdlib code to determine that.
Perhaps 40% of the stdlib documents the error type it returns in a message (like 'os.Chdir' always returns '*os.PathError'), but for the rest, good luck. Want to figure out what errors you might have to check for 'tar.Writer.Close()'? Well, the docs says "returns an error", the interface is "error", you have to read hundreds of lines of code to figure out the possible concrete types it could be. Maybe 15% of the time, you end up having to string-match on error messages because the error var or type is unexported.
Well, it's structural, so you don't need other packages to implement an interface rather you need them to accept an interface. That also makes it clear it's a bigger ask - you're not asking a dependency "please also do X" but instead asking "please never need to more than Y".
> Want to figure out what errors you might have to check for 'tar.Writer.Close()'? Well, the docs says "returns an error", the interface is "error", you have to read hundreds of lines of code to figure out the possible concrete types it could be.
The concrete types it could be are unbounded, because `tar.Writer` wraps arbitrary `io.Writer`s. If you need multi-pathed error handling (usually people don't and are just making it out of habit!), worry about what things can do, not what they are.
When I'm looking at an error, it's typically for one of two reasons:
1. To set a correct status code, such as http 5xx (internal server error, our disk flaked) or a 4xx (user error, you gave us invalid input).
2. To provide a better error message, such as to localize it into an error string.
If you're building CLI tools for yourself, sure, every error is fatal and you can read english so you don't need either of those. For most go projects, both of those are relevant concerns for a large number of error paths.
Go's type-system does not help you at all.
Speaking of...
> Well, it's structural, so you don't need other packages to implement an interface rather you need them to accept an interface. That also makes it clear it's a bigger ask - you're not asking a dependency "please also do X" but instead asking "please never need to more than Y".
Yup. That is a big problem. That's the root of the error problem too, where every package returns the stdlib error interface, which is a tiny subset of what you usually want.
For this it's simple to wrap them at return site in something that offers `HTTPStatus() int` and check for implementing that interface, not any concrete types, in your handler.
Also, those error paths should be dangerously hard to mix in the first place, you shouldn't be letting invalid input anywhere near the disk to begin with.
Re. logging interfaces, I think you've missed the point. You want everyone to accept narrow interfaces so you can use the logger you want. You also want everyone to return wide error interfaces so you can categorize the entire universe of possible errors as you want. In the end this isn't a technical problem, it's an "I want everyone to cater for my use case" problem.
It's not though, the return site is inside the go stdlib. I cannot annotate it with new methods.
The only way to figure out how to translate all errors (whether to status codes or to other readable messages in localized languages) is to read the code and figure out what errors it might return.
> you want everyone to return wide error interfaces so you can categorize the entire universe of possible errors as you want. In the end this isn't a technical problem, it's an "I want everyone to cater for my use case" problem.
This is a technical problem. In Rust, libraries define error types and return "Result<T, MyErrorType>", which lets a library author decide what errors are interesting or not. If I think they have not classified an error that is useful for a caller, I can file an issue.
In java, exceptions have types, and I can know what types of checked exceptions a function might throw, and can similarly ask for more specific exceptions, or modify the library to provide them.
In go, _every_ library, due to go's error handling idioms and some mis-features of nils/type-inference, returns the most useless error type possible, the 'error' type, and I have to constantly read docs or code to figure out what types it might be.
I don't see how this isn't a technical issue with the language that, at the type-system level, it makes it an anti-pattern to return concretely typed errors in a way the type system can recognize them.
I don't agree with how you're characterizing what I'm saying as being "catering to my use-case".
Do you just never actually need to classify an error? Is it somehow weird to want to be able to provide a localized error to a user? Doesn't everyone have these problems too?
type httpClientError struct { error }
func (err httpClientError) HTTPStatus() int { return 400 }
func (err httpClientError) Unwrap() error { return err.error } // if needed
> Do you just never actually need to classify an error?
Infrequently, and virtually never for errors types I didn't write myself (other than a tiny number of sentinels like UnexpectedEOF or DeadlineExceeded).
> Is it somehow weird to want to be able to provide a localized error to a user?
Yes, it's unusual for error details (rather than e.g. outcomes) to be localized for display directly to non-technical end users. This is also true of exception messages in Java. General-propose desktop client software is rarely written in either language.
I think you're too focused on the specific issue to see my general point about interface size.
Even within your own program, you now have to read the code in "httputil" to understand what possible error types can be returned.
It's idiomatic to never return concrete error types, whether from the stdlib, or third party libraries, or even methods within your own program.
Even for types you do write yourself, you still have to either memorize what errors each method may return, or you have to constantly refer to docs or source code reading.
Clearly you think this is fine and go's type system is good enough for your use-cases, but every larger go program I've worked with, error handling has been painful since the errors are effectively untyped.
I assume we must have worked on different types of go projects if you haven't run into pain with this.
> Yes, it's unusual for error details (rather than e.g. outcomes) to be localized
I absolutely agree that it's outcomes which are localized, but to determine _outcomes_, you have to classify errors. If the _outcome_ is "File doesn't exist", that's a different error than "permission denied", so you need to classify. But the type you have is "error", so you have to constantly refer to docs.
Nonetheless, Go does provide ways to check whether an error either is or can do what you want, and ways to annotate errors with logic specific to your program. An `httpClientError` is an `error`. When you get an error from a source you want to treat as a 400, you wrap it and return it, as an `error`. You use `errors.As` on it as a concrete type, or an `interface { HTTPStatus() int }`, to use the method you've added.
Regarding localization, which is a significantly different problem - the outcome is e.g. "file can't be opened". It's hard to write good error messages based on the language's error messages but this is not a Go-specific problem at all. Either you constrain your operations to the point you can bound all your error types, or you don't and report the outcome + raw message instead of trying to localize causes. And yes, this is an unusual space to be using Go or Java.
Since you mentioned Rust, we could also consider how it solves the problem - `Write` returns a `Result<usize, io::Error>` - `io::Error` has a (almost uselessly long and yet still) non-exhaustive `ErrorKind` - the last of which is `Other`, "used to construct your own Errors that do not match any ErrorKind." I.e. even in Rust's type system, they punted because otherwise you can't easily compose anything.
- Do you want to reverse bytes, or codepoints?
- Do you want to reveres codepoints, or grapheme clusters?
- Do you really want to reverse grapheme clusters, or do you want to reverse some grapheme clusters while leaving e.g. sequences of control characters in the same order?
- Do you really want to reify any of this rather than iterate backwards in the existing memory?
C++: reverse(str.begin(), str.end());
Dart: str.split('').reversed.join();
Java: new StringBuilder().append(str).reverse().toString();
JavaScript: str.split('').reverse().join('');
PHP: strrev($str)
Python: ".join(reversed(str))
Rust: str.chars().rev().collect()
(What do I mean by wildly different things?
C++: Swaps the string's contents in-place, and probably breaks any multi-byte code units unless you've got a parameterized std::string at hand.
Dart: Makes a new string but has to round-trip via an array, because... it doesn't have a string reverse? This seems like a really bad argument for your side!
Java: Reverses codepoints, but the fact you have to round-trip through a StringBuilder to handle this is also telling.
JavaScript: Same comments as Dart, but I believe this is broken, it will reverse surrogate pairs incorrectly.
PHP: Good luck figuring out what this does depending on your platform, locale, and moon phase.
Python: Another codepoint reverse, again not via strings but a lazy sequence, and also not even idiomatic - use `str[::-1]`.
Rust: And finally again... not a string reverse.
You want a Go slice reverse? You can get a perfect one post-generics.)