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Comment by knorker | Hacker News Reader

You're assuming that the code was written exception safely. E.g.

    mu.Lock()
    foo := bar[baz]    // <- throws exception / panics
    mu.Unlock()

Go is sold as a language without exceptions, so people don't write exception-safe code. Which is fine, except when exceptions are actually caught.

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That wouldn't pass a code review where I work... Use a defer to do the unlock

Does defer get called on panic? I thought panic cancels all further execution

Yes it does, which is why recovering from a panic can be done in a deferred function. The go runtime maintains enough metadata to track what deferred functions need to be run while unwinding the stack.

I would also not allow it. I'm saying the problem is that core Go developers say "Go doesn't have exceptions", which is manifestly false, but causes people to not write exception safe code.

But despite you and me, I'm saying there's a lot of broken code out there because of this doesn't-but-actually-does misinformation.

And it's very annoying that you have to tell people to do:

    var i int
    func() {
      mu.Lock()
      defer mu.Unlock()
      i = foo[bar]
    }()

Clean code, that is not. (even if you simplify it by having the lambda return the int)

This is like the biggest thing scaring me away from Go. This half-assed "we don't use exceptions, so you shouldn't have to care about it, except when we do, so you still must write proper defers, which are now doubly verbose because nobody considered it a primary use case"... In any other language, a mutex outside a using/with/try-with/RAII would be instantly flagged in code-review or linter tools. In many cases even hard to write incorrectly, due to entering context being only way to acquire the lock.

Now this middle ground leaves you having to write triple verbose if err != null on every third line of your code and still not be safe from panics-that-shouldnt-have-been-panics.

As parent says, the only way panics can ever work is if the top-level never catches and recovers from them. I'm no expert in go but that would mean in such perfect world, defer should hardly ever be needed at all, not even for locks? Only for truly external resources? But now with popular web servers doing such recovery, the entire ecosystem got polluted and all need to handle it?

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