Finding error type for `errors.As` and `errors.Is`

[Michael Schaller]

Hi everyone,

I often encounter deep error chains where errors are wrapped across several Go packages and that makes it often hard to find a usable error type to use with `errors.As` or `errors.Is`.

Could it make sense to add an `errors.Chain` function to Go that returns a slice with tuples of error type (reflect.Type) and the respective error?

Quick example:

https://play.golang.org/p/hDW0_6P7O2Y

Best,

Michael

[roger peppe]

On Wed, 31 Mar 2021 at 18:05, 'Michael Schaller' via golang-nuts <golan...@googlegroups.com> wrote:

Hi everyone,

I often encounter deep error chains where errors are wrapped across several Go packages and that makes it often hard to find a usable error type to use with `errors.As` or `errors.Is`.

Could it make sense to add an `errors.Chain` function to Go that returns a slice with tuples of error type (reflect.Type) and the respective error?

Unfortunately that's not possible in general because errors in the change can implement their own `As` and `Is` methods, so an error can appear

to have some type T in the chain (i.e. errors.As(new(T)) returns true) without actually having that type in the chain.

For example: https://play.golang.org/p/-IAKMrD8FlG

It's a shame in my view, but that's what we've got.

  cheers,

    rog.

Quick example:

https://play.golang.org/p/hDW0_6P7O2Y

Best,

Michael

--
You received this message because you are subscribed to the Google Groups "golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/acab291d-21bc-4c84-a19a-7f9901cc8035n%40googlegroups.com.

[Michael Schaller]

Roger, I think you slightly misunderstood me. ;-)

It is true that `As` and `Is` methods can be used to allow `errors.As` and `errors.Is` to handle error types that aren't actually in the error chain.

However my question was if an `errors.Chain` function which returns details about the error types and values in the error chain would be a worthwhile addition to Go's `errors` package.

[Jonathan Amsterdam]

You can write such a function yourself. For that reason and since it would be rarely useful, I don't think it's likely to become part of the standard library.