Has anyone made a custom rule/does a default one exists that check for `when` statement orders? I’m ...

# detekt

[Luca Nicoletti]

Has anyone made a custom rule/does a default one exists that check for when statement orders? I’m looking to have all objects of a sealed class/interface coming first, then the data classes, so my when(s) would look like:

when (a) {
   object1 -> {}
   object2 -> {}
   object3 -> {}
   is dc1 -> {}
   is dc2 -> {}
}

And not with is mixed between all the statements

[Chris Lee]

branches in a when expression are evaluated in the order provided; would be questionable to force an arbitrary order that may not align with the logic of the expression.

[Luca Nicoletti]

Can you explain better? The page says

matches its argument against all branches sequentially until some branch condition is satisfied.

Meaning that it try from the first until there’s a match, then stops, right?

[Chris Lee]

that’s correct.

[Luca Nicoletti]

If I have a sealed interface with 3 objects and 2 data classes my instance will be either an object (only one), or a data class

[Luca Nicoletti]

I don’t see a problem in having some code order there 🤷🏼, trying to match object firsts, and then data classes

[Chris Lee]

yes, but it can satisfy any number of conditions. For example, if classes implement several interfaces (A, B, C) you may have logic where is C is checked before is A. Also, performance may be a consideration - will often organize when expressions knowing that certain conditions are frequently hit (or not).

[Luca Nicoletti]

We don’t have that structure for now, so, do you know if there is a way or not?

[Chris Lee]

No idea if there is a way. Suggesting it won’t be common or prudent for the reasons above.

[Luca Nicoletti]

Thanks 🙂

[Brais Gabin]

That's completely doable but as far as I know there's nothing like that implemented.

[Brais Gabin]

In general I prefer to group the when in a logical order. First loading state, the errors and then success. Or something similar. The problem is that a rule is difficult to umpteenth to do something like that. Is the same as keep the related functions together.

[Luca Nicoletti]

Any suggestions/hints on how to get started with that?

[Brais Gabin]

Use this template https://github.com/detekt/detekt-custom-rule-template and look at detekt for a rule that does something similar. In your case a rule related with when. Copy&paste that rule to your project and edit it until it does what you want.

[Brais Gabin]

In general is a really good idea to write the test first.

[Brais Gabin]

And I'm not a tdd fan. Tests first works really well with detekt