alt Hacker News> Indeed, you can absolutely handle some cases with combinations of `errors.Is` and `fmt.Errorf` instead of implementing your own error.
Not "some cases" but "almost all cases". It's a categorical difference.
> Most of the Go code I've seen (including big parts of the standard library) doesn't document how one could handle a specific error. Which feeds back to my original claim that "errors are primarily meant to be logged and that you have to get out of your way to develop errors that can actually be handled".
First, most stdlib APIs that can fail in ways that are meaningfully interpret-able by callers, do document those failure modes. It's just that relatively few APIs meet these criteria. Of those that do, most are able to signal everything they need to signal using sentinel errors (ErrFoo values), and only a very small minority define and return bespoke error types.
But more importantly, if json.Marshal fails, that might be catastrophic for one caller, but totally not worth worrying about for another caller. Whether an error is fatal, or needs to be introspected and programmed against, or can just be logged and thereafter ignored -- this isn't something that the code yielding the error can know, it's a decision made by the caller.
> Not "some cases" but "almost all cases". It's a categorical difference.
Good point. But my point remains.
> First, most stdlib APIs that can fail in ways that are meaningfully interpret-able by callers, do document those failure modes. It's just that relatively few APIs meet these criteria. Of those that do, most are able to signal everything they need to signal using sentinel errors (ErrFoo values), and only a very small minority define and return bespoke error types. > > But more importantly, if json.Marshal fails, that might be catastrophic for one caller, but totally not worth worrying about for another caller. Whether an error is fatal, or needs to be introspected and programmed against, or can just be logged and thereafter ignored -- this isn't something that the code yielding the error can know, it's a decision made by the caller.
I may misunderstand what you write, but I have the feeling that you are contradicting yourself between these two paragraphs.
I absolutely agree that the code yielding the error cannot know (again, with the exception of panic, but I believe that we agree that this is not part of the scope of our conversation). Which in turn means that every function should document what kind of errors it may return, so that the decision is always delegated to client code. Not just the "relatively few APIs" that you mention in the previous paragraph.
Even `text.Marshal`, which is probably some of the most documented/specified piece of code in the stdlib, doesn't fully specify which errors it may return.
And, again, that's just the stdlib. Take a look at the ecosystem.