Yes, manual tagging doesn't provide type safety. That's why I said some people are disappointed that Go doesn't have sum types. There isn't even a convoluted workaround either, at least not a full one.
It is not so much a matter of lack of type safety, it is forgetting to implement an application requirement.
Even an advanced type system capable of formal proofs isn't going to help you if you've forgotten the requirement when defining the types. And if you are using a language with a lesser type system (Go, Rust, any language you are likely to use in the real word), and haven't forgotten the requirement, then you would have encoded that knowledge in tests instead, making the forgetfulness in implementation ultimately immaterial. After all, there is no practical difference between learning that you forgot to implement logic by the compiler telling you or the test suite telling you.
So, we can infer that the OP is talking about where one straight up forgot about the requirement from start to finish. I'm skeptical that there is any technical solution to that problem, but sum types most certainly isn't it.
There is a point at which even dependent typing won't save you, but sum types are a useful tool to reduce negligence. Don't let perfect be the enemy of good.
Sum types are useful tool, but they are not helpful in this particular case. There is nothing about sum types that would help avoid this problem in the slightest. Perfect need not be the enemy of good, but good is not equivalent to not even trying.
This is not a general "wouldn't it be nice of Go had..." thread. We are talking about a specific problem.
I'm not really sure what your point is then. We should have comprehensive tests and therefore error checking isn't special compared to other programming mistakes? I think we should both have tests (don't skimp on them if given time, of course) and use tools like sum types to write more robust programs from the get-go. Errors can even be treated like other values using sum types; that raises the bar universally instead of just improving error checking.
If you're going to invoke some abstract "the programmer doesn't know what they're doing" situation, I'm not sure how to continue this discussion. Even testing may not help in that case. Things are going to slip through the cracks. Having features like sum types is a way to generally reduce the likelihood of such semantic errors.
Besides, the original topic was that Go doesn't make its error handling very foolproof. Sum types help with that and don't make error handling special, so I really don't see your point. Why not write everything in Brainfuck then? Everything is uniform and simple. Well, it's simple to the point that it's way too easy to make mistakes.
The original topic was, stated quite explicitly, that it is easy to forget to handle errors in Go. There is nothing about sum types, as defined, that addresses that concern.
Like we established in my very first comment, well before you even showed up, the handling forgetfulness problem exists for all types. That would include a hypothetical (tagged) union type. I did question if you were using some other definition of sum types, as there isn't a great consensus on what sum types actually mean, but you did confirm you were thinking of tagged unions...
But it must be that you didn't actually mean tagged unions. What is the definition of sum types that you are using here that would help with the stated problem?
There may be a misunderstanding. I say "sum type" to mean something along the lines of Rust's enum: a value stores both a tag and its data, and pattern matching distinguishes the variants (like a switch statement). It's a tagged union where the interpretation of the tag is managed by the compiler. The underlying value can't be used without extracting the variant with pattern matching. Even if the success and failure variants both contain an integer, you can't add an integer with this value.
So you're saying the programmer forgets to use the return value at all. There are linters, documentation, and basic common sense. This is not at all a relevant issue, or else there are serious issues with the programs you see. Why are you discussing whether Go's error handling needs improvement if your imagined programmer can't even program? Well, I've spent enough time on this thread.
> So you're saying the programmer forgets to use the return value at all.
That's what the original commenter said. Logically, how else could you forget to handle the error? The compiler will bitch and moan if you do capture the result and then don't do anything with it. You did take the time to read the thread before replying, yes?
> This is not at all a relevant issue
It must be, else how do you explain the many comments you wrote trying to explain how sum types solves the problem? Even while I continually told you they don't.
> Why are you discussing whether Go's error handling needs improvement if your imagined programmer can't even program?
I said that it doesn't need improvement because in practice your tests will catch the problem immediately anyway. I even said that it is probably fundamentally impossible for there to be technical solution to the problem.
And the rest of the time was telling you that sum types cannot solve the problem, despite your constant urging. I am still not clear how you think sum types solve the problem.
