[preseinger]

Right, all of these are good points, but the problem is that the "failure boundary" of a panic is the entire process. You can't constrain it, or assume that it's scoped to a single goroutine. Errors do not have this property.

[groestl]

> the "failure boundary" of a panic is the entire process.

This is trivially falsifiable by panicking yourself and immediately recovering. Neither failure domain nor failure boundary need to align with the entire process.

[preseinger]

The impact of a specific panic does not extrapolate to the impact of all panics, and my claim is not falsified by such an example. Panics are defined by the language to represent unrecoverable errors.

    func (x *Thing) Method() {
        x.somethingThatPanics()
        x.somethingThatAssumesTheAboveDidntPanic()
    }

Recovering from a panic thrown by Method invalidates the state of the Thing which threw that panic. If that Thing is shared among concurrent actors, the entire program state is invalidated.

[groestl]

> If that Thing is shared among concurrent actors

You're adding preconditions to your claim.

> the entire program state is invalidated.

No, the state represented by a connected graph of variables accessible by the concurrent actors is tainted. This is hardly "the entire program state". Often it's just a few cache entries.

Also, see my first, most important, bullet point:

"* Make sure you support properly unrolling the stack."

Which means a request to Thing errored out, but it never enters an invalid state. If you fail at that, all bets are off. But then you're dealing with a mediocre codebase anyway.

And finally, let me rewrite your example to something, that I see much more often in real life code, which problematic _even without concurrent actors_ because somethingThatAssumesTheAboveDidntReturnAnError might do horrible things all by themself:

func (x *Thing) Method() {

x.somethingThatReturnsAnError()

x.somethingThatAssumesTheAboveDidntReturnAnError()

}

[preseinger]

I'm not sure how to respond to this. You seem to believe that panics express problems which are constrained to the call stack which instantiated the panic. This isn't true. But I'm not sure how to express this to you in a way that will convince you. So I guess we're at a stalemate.

[groestl]

> You seem to believe that panics express problems which are constrained to the call stack which instantiated the panic.

Not inherently, but it's your job as a developer to make sure this is the case, that's what:

"* Make sure you support properly unrolling the stack."

means.

In case you're dealing with unknown code it's your job to find out what the connected graph of potentially tainted objects is and discard them. That's what "keep a clean failure boundary" means.

If you can't, because you don't want to (short lived process, prototypes) or are unable to (hairy ball of code), tearing down the process is indeed the only option and a sane fallback choice made by the language designers. But it's not necessarily a hallmark of robust software.

I hope I had a final shot to clear up what I meant, thanks for the discussion anyway.

[preseinger]

In Go when some code writes `panic` it is expressing an error condition which should not be intercepted by callers and is expected to terminate the process. A panic is not an error, and panics should not be recovered as if they were errors.