A "maybe" type is logically incompatible with "subatomic I/O". When a sized-read() syscall results in a short read AND a raised error. The only sensible thing to do is to return both.
I am not familiar with Rust, but looking around the docs on Read [https://doc.rust-lang.org/std/io/trait.Read.html#errors] I see:
> If an error is returned then it must be guaranteed that no bytes were read.
Could someone elaborate how a system can satisfy this guarantee, seems impossible...?
That's an API choice. There's no technical reason at all why you couldn't return some kind of error AND read data if you wanted, you'd just have to make your Error type a product type.
That’s hardly a reason not to include a maybe type. In that particular case, instead of a maybe you can use a combination of sum and product types or just an additional ShortRead type.
NormalRead | ShortRead | Error
This case is also an example of why go’s idiom of using error value or return value doesn’t always work.
If you had a maybe type and a general sum type it would be clear when a function was going to return either or both.
You could write sum type that handles multiple cases.
Value Error ValueAndError
A maybe type would have been a much better solution. I wish people would just accept that go's error handling is a stopgap solution instead of pretending it's a good (or the best) solution.
I'd bet a substantial amount that go in 10 years ends up with pattern matching and sum types.