What return type should a Scala method have if it can throw/return errors but has Unit return type?

Question

So usually when we run a method that can both fail and return a value, we can encode our method return type as Either[SomeErrorType, ReturnType]. But many times

Answer 1

One more option that hasn't been mentioned yet is Validated from cats. All the options mentioned so far (Try, Either, Option) are monads, while Validated is an applicative functor. In practice this means you can accumulate errors from multiple methods returning Validated, and you can do several validations in parallel. This might not be relevant to you, and this is a bit orthogonal to the original question, but I still feel it's worth mentioning in this context.

As for the original question, using Unit return type for a side-effecting function is perfectly fine. The fact this function can also return error shouldn't get in your way when you define the "real" (right, successful, etc.) return type. Therefore, if I were to select from your original options, I'd go for Either[Error, Unit]. It definitely doesn't look odd to me, and if anyone sees any drawbacks in it, I'd like to know them.