Few questions

[qwerty2586]

Hello, i am using package for a while in several projects and I am refactoring old code to get rid of underscores. I have stumbled to few issues that are missing from documnetation.

Simple way to overwrite errors?

Or just annotate single try, so i would be able to recognize type of error in error hadler. And if possible check if annotation is present.

StacktraceWriter doesnt print annotations. Is this intentional?

I thought that purpose of StackTraceWriter is to setup and forget about printing errors everywhere.

Example to use try.Is()

I am not sure how to use it. Also more examples please.

Thank you for library. It helps with writing much better code.

[lainio]

Hello, and thank you very much for your comments and questions. They are highly appreciated!

Simple way to overwrite errors?

The current err2 package follows the Go2 try-proposal, where you add as many deferred error handlers as your function needs.

If I understand your question right, you would like to know what was the specific try.To which triggered the error. The preferred (and only) way is to use as many deferred err2.Handle or err2.Returnf. The order of the handlers tells what to do in the particular error handler. Please see the following playground. There is just one err2.Handle for the cleanup. The first one, err2.Returnf, annotates the error. Both are called when there is an error after target file creation.

If you wrap the error in any handler, you can use Go's errors.Is function to check if the wrapping is already done.

Please see the following playground example about how to 'override' or wrap the current error. The err2.Handle handler now replaces the function's first err2.Returnf statement and annotates the error slightly differently.

StackTraceWriter should print annotations. If not, it's not intentional

Where stack tracing is on, please see this altered playground. Please also notice that there are two different stack traces. The highest level of the call stack main function naturally has most of the error annotation:

---
copy /tmpfs/play_not_exist /file_in_root: open /tmpfs/play_not_exist: no such file or directory
---

The annotation is shorter in the CopyFile function itself because it hasn't yet annotated the error when the automatic StackTracing prints it.

---
open /tmpfs/play_not_exist: no such file or directory
---

I'm still open to suggestions. For our use cases, this has been enough, and to be honest, it's easiest to implement, and it has been most helpful for debugging.

Example to use try.Is()

About the examples, please see the official err2 Go documentation.

About the try.Is(), the following code block is taken directly from our project:

	...
	myAE, err := d.AEndp()
	if !try.Is(err, ErrNoData) {
		return NewDoc(d, myAE)
	}
	return NewDoc(d, ae)

try.Is return true if err is (internally uses Go's errors.Is) ErrNoData and it also checks the other errors as well, i.e., if any other error happens, it behaves like regular try.To.

Summary of try.Is: it only return false when err == nil and if err == ErrNoData it returns true so we can make a decision.

I hope I could have been a help. If you have any other questions or comments, please let me know.

Best regards,
-Harri