Hey guys, I’m playing a little bit with simulated ...

# random

[Davide Giuseppe Farella]

Hey guys, I’m playing a little bit with simulated intersection types.

My use case: I have different classes that share the same pieces of business logic, for example can handle sorting, searching, etc
Those operations share some dependency, for example, a StateHolder.
An example:

class ClassOne(
  private val stateHolder: StateHolderOne
) {
  
  init {
    stateHolder.getSearchQuery()?.let(::search)
    stateHolder.getSorting()?.let(::sort) 
  }
  
  fun search(query: String) {
    stateHolder.setSearchQuery(query)
    ...
  }

  fun sort(sorting: Sorting) {
    stateHolder.setSorting(sorting)
    ...
  }
}

class ClassTwo(
  private val stateHolder: StateHolderTwo
) {
  // may or may not have search, sort, and others
}

What I wanna do, is extract those pieces of logic in reusable components, like Searchable, Sortable etc, thus each would depend on a (part of) StateHolder, e.g. SearchStateHolder

This is quite easy, but I don’t like easy stuff 🙂
My problem is that I would need to do something like this

class ClassOne(
  private val stateHolder: StateHolderOne
) {
  
  val sortable = Sortable(stateHolder, /* other deps */)
  val searchable = Searchable(stateHolder, /* other deps */)
  val other = Other(stateHolder, /* other deps */)
  // etc
}

Indeed, I want to declare a single Delegate, that features all the operations I need/are supported by a given StateHolder
Something like this

delegate(
    Searchable,
    Sortable,
    stateHolder = stateHolder // -> StateHolderOne: SearchableStateHolder, SortableStateHolder
) // -> Searchable & Sortable

Well, I got it working, by forcing a bit the compiler https://pl.kotl.in/534LENaCV
But I got two problems:
• It does work with K2, but with Kotlin 1.9.23 I got this on stateHolder = stateHolder

Type mismatch: inferred type is Searchable but Sortable was expected

Type mismatch: inferred type is Sortable but Searchable was expected

• I’m fine to force the compiler for where I add this borderline code, but I would gladly avoid suppressing INCONSISTENT_TYPE_PARAMETER_VALUES in the client code
Got any idea?

[Davide Giuseppe Farella]

For clarity: this part is temporary, just to test the API surface, I will need t change it, otherwise it would completely destroy the purpose of the experiment 😄

CombinedDelegate(
    searchable = RealSearchable(stateHolder as SearchableStateHolder),
    sortable = RealSortable(stateHolder as SortableStateHolder)
) as D

In another project I did something like this:
1. https://github.com/fardavide/CineScout/blob/e9a64272b1d32635217d1be15f583603ce68c6[…]lin/cinescout/details/domain/usecase/GetScreenplayWithExtras.kt
2. https://github.com/fardavide/CineScout/blob/e9a64272b1d32635217d1be15f583603ce68c6[…]/commonMain/kotlin/cinescout/details/domain/usecase/GetExtra.kt