it s very javascripty in that you have to go back and forth

Question

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 · Answer

I don t think there s any big performance tradeoffs there at all quite the contrary in fact

pakoito · Answer

reference check vs ~~instaceof~~ virtual dispatch Maybe < removed > knows something that we don t smile

louiscad · Answer

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 · Answer

gt 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 · Answer

``` sealed class Tristate lt A gt fun lt B gt fold fu gt B fn gt B fa A gt B object Uninitialized Tristate lt Nothing gt override fun lt B gt fold fu gt B fn gt B fa A gt B = fu object Nullish Tristate lt Nothing gt override fun lt B gt fold fu gt B fn gt B fa A gt B = fn data class Option lt A gt val a A Tristate lt A gt override fun lt B gt fold fu gt B fn gt B fa A gt B = fa a ```

pakoito · Answer

That isn t even an instanceof check as a when would do it s just a virtual call I believe May be wrong

pakoito · Answer

still more expensive than reference checks for sure

pakoito · Answer

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 · Answer

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 smile <https github com arrow kt arrow blob master modules effects arrow effects data src main kotlin arrow effects IORunLoop kt L12 L15>

louiscad · Answer

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 · Answer

gt 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 smile

pakoito · Answer

same thing put on a funny talk <https www destroyallsoftware com talks useing youre types good>

louiscad · Answer

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] · Answer

gt ~~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 disappointed

Dico · Answer

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