Unit return types

[JorgeCastilloPrz]

When you're writing code in an FP manner, you want to keep all effects under control. Functions that return Unit are effectful by definition, since otherwise they'd do nothing. On their bodies, they always access the external world, as in printing, logging, network queries, database reads / writes, modifying the value of class properties... etc.

Action points

• The redundant Unit return type is an IntellIJ IDEA Inspection. Unit return types are never redundant from an FP perspective, since they make function "referentially transparent". The function states what's it doing by looking at it's input and output types, so best thing we can do is to give feedback to Arrow users about how to disable it in README and "Quick start" docs section as also suggested for Redundant suspend modifiers #1385. Also include a link to the official intention action docs.

• Apart from the IntellIJ IDEA Inspection, Ktlint also complaints about Unit return types regardless of where they're used. That's also something we could suggest users how to disable on their ktlint configurations, since from an FP perspective it's always important to declare return types regardless of what they are, so it's explicit that the function has side effects inside.

[pakoito]

I'd suggest reaching out to twitter to see if someone is interested in owning this space.

[JorgeCastilloPrz]

@Tylos will tackle this during next quarter.

[Tylos]

Opening PR to document how to disable the check for IDEA

Ktlint is still pending until certain rules can be disabled. It is currently in PR - pinterest/ktlint#503

Should it be moved to a separated issue @JorgeCastilloPrz ?

[JorgeCastilloPrz]

Yep it'd be nice if we can add an issue for it then create a Marlow goal. As soon as support for disabling global rules is released to ktlint it'll be an easy one to tackle.