it’s very javascripty in that you have to go back ...

# coroutines

[pakoito]

it’s very javascripty in that you have to go back and forth with reference comparison and unchecked casts to make it work, with performance as a big tradeoff compared with a sealed class or a nested Option

[louiscad]

I don't think there's any big performance tradeoffs there at all, quite the contrary in fact.

[pakoito]

reference check vs instaceof virtual dispatch. Maybe @[removed] knows something that we don’t 😄

[louiscad]

There's no instanceof nor is check here. Reference equality and unchecked casts are used, and these are way cheaper than any complicated Option type you can come up with and nesting it.

[pakoito]

there’s any big performance tradeoffs there at all

I thought you meant compared to sealed classes, which depending on implementation may be a direct call into one of the branches instead of doing the ifcheck

[pakoito]

sealed class Tristate<A> {
  fun <B> fold(fu: () -> B, fn: () -> B, fa: (A) -> B)

  object Uninitialized: Tristate<Nothing> {
     override fun <B> fold(fu: () -> B, fn: () -> B, fa: (A) -> B) = fu()
  }

  object Nullish: Tristate<Nothing> {
     override fun <B> fold(fu: () -> B, fn: () -> B, fa: (A) -> B) = fn()
  }

  data class Option<A>(val a: A): Tristate<A> {
     override fun <B> fold(fu: () -> B, fn: () -> B, fa: (A) -> B) = fa(a)
  }
}

[pakoito]

That isn’t even an instanceof check as a when would do, it’s just a virtual call, I believe. May be wrong.

[pakoito]

still more expensive than reference checks, for sure

[pakoito]

you’re trading off strict types for some perf, which is what I mean by “going javascript” where everything is Object like in a dynamic language

[pakoito]

we use it on Arrow too, but it’s not to avoid a tristate but to interpret the function calls captured by IO where we’d need to match parameter types with function objects on a recursive loop and that’s just not feasible 😄

https://github.com/arrow-kt/arrow/blob/master/modules/effects/arrow-effects-data/src/main/kotlin/arrow/effects/IORunLoop.kt#L12-L15

[louiscad]

Comparing a reference check to JavaScript is a bit excessive IMO.

Reference check to an internal object is a usual light pattern that is also used in stdlib's lazy FYI.

[pakoito]

Comparing a reference check to JavaScript is a bit excessive IMO.

Not reference check, going down to Any? to store a value on a variable so the variable can contain an arbitrary value of an unrelated type. So, dynamic typing of variables 😄

[pakoito]

same thing, put on a funny talk: https://www.destroyallsoftware.com/talks/useing-youre-types-good

[louiscad]

Well, that happens to a lot for generic containers, and as long as that doesn't spread everywhere like it does in JavaScript, I don't think it's a bad thing. The public API is still typesafe, and its behavior is tested.

[Vsevolod Tolstopyatov [JB]]

instaceof virtual dispatch

Virtual dispatch is not an issue here.
But allocations of Option on each value and lambdas for fold are.
One could think of Result-like inline class, but then boxing kicks in 😞

[Dico]

Also used in coroutine intrinsics to indicate suspension. Not sure why it's compared to js or sealed class for performance. It's implementation detail.