Hacker News Reader

Comment by shaan7 | Hacker News Reader

Note that this can quite problematic in scenarios where the caller wants to inspect the error (example: was the error an http timeout? or a server error?). Returning the error and letting the topmost call site handle that is usually better.

View on HN

That's what `errors.Is` is for. https://pkg.go.dev/errors#Is

It would be interesting if anyone used error types in Go, but you'll be hard pressed to find libraries that do. return fmt.Errorf() all the way.

In my experience, errors returned by the standard library and recent third party packages are fairly well discernible, although not in all cases.

Note that you don't need custom error types, just exported Error instances. These were in use even before wrapping was introduced with Go 1.13 (2019); one had to compare or type-assert directly instead of unwrapping.

You can use %w in fmt.Errorf to accomplish this.

Not really. If the original error is `fmt.Errorf("divide by 0")`, no amount of `fmt.Errorf("failed to divide: %w")` will help anyone programmatically recognize the error.

Yup, fair point, I thought we were talking about libraries replacing errors to obscure the original, which absolutely happens. Lots of libraries (e.g aws-sdk) do use typed errors, so wrapping them correctly for smaller libraries that compose them is important.

No you should use errors.Is(err, http.ErrHandlerTimeout) instead of simple equality.

Thanks (and to mseepgood as well). TIL :)

Reply on news.ycombinator.com