On Wed, Sep 2, 2020 at 12:20 PM 'simon place' via golang-nuts
<golang-nuts@googlegroups.com> wrote:
>
> OK, i think i have it;
>
> basically he root of it was i wasn't thinking properly about how errors
> need/should be implemented as immutable. Unwrap is basically a state getter.
> (no setter for the wrapped error.)
>
> so it seems to me that custom and fmt.Prinf("%w") wrappers have different use
> cases:
%w is not a formatting verb, so fmt.Prinf("%w") is not valid.
Instead of creating a separate MyErr struct, you could've done:
err1:= errors.New("error")
err1= fmt.Errorf("fmt wrapping: %w",err1)
fmt.Println(err1)
err2:=errors.New("error")
err3= fmt.Errorf("Wrapped: %w",err2)
// Here, err3 is an error wrapping err2
fmt.Println(err3)
>
> * fmt.Printf(%w) is just to add more text to an error, because errors are
> immutable its needed.(unless you have custom error types and are local to
> them, then you could just edit their state.)
>
> * custom wrapping types, unlike fmt.Printf(%w), create error 'classes' for
> testing against and have utilities to help deal with unknown depths of
> wrapping.
>
> since i was only dealing with one level, i probably should have avoided
> wrapping entirely, but now i know!
>
> this does seem as if its a pattern that might come up elsewhere, so good to
> understand clearly (unless i'm still off about something above).
>
> thanks for help.
>
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