is there a way to add locally on the fly additiona...

# getting-started

[elect]

is there a way to add locally on the fly additional boundaries to a type of a local variable? That is, I have value: Value<N : Number> and I want temporarily to cast is as Value<N : Number, N: Comparable<N>?

[Laertes Moustakas]

Think you need to do something like:

fun whatever(value: Value<N>): T
    where N: Number,
          N: Comparable<N>

Though I think Number implements Comparable itself.
Apparently not, all built-in Number implementations just so happen to implement Comparable too.

[Laertes Moustakas]

See also: https://kotlinlang.org/docs/generics.html#upper-bounds

[Youssef Shoaib [MOD]]

Would value as Value<Comparable<N>> not work? If not, maybe this thread from long ago about intersection types could help?
I'm thinking something along the lines of:

sealed interface TypeWrapper<out T> {
  companion object: TypeWrapper<Nothing>
}
@Suppress("BOUNDS_NOT_ALLOWED_IF_BOUNDED_BY_TYPE_PARAMETER")
@OptIn(ExperimentalContracts::class)
// R is automatically inferred to just be T1 & T2. 
// the callsite doesn't have to supply a type for R since you can't explicitly write out intersection types.
fun <T1, T2, R> intersection(): TypeWrapper<R>
        where R : T1, R : T2

= TypeWrapper
 
inline fun <reified T> Any.cast(type: TypeWrapper<T>): T = this as T
 
fun main() {
  val value: Any = 5
  println(value.cast(intersection<Number, Comparable<*>, _>()).toDouble())
}

I think you can edit that and perhaps make another function that takes a TypeWrapper<T> and outputs a TypeWrapper<Value<T>> and use that for the cast.
Let me know if that works, and don't hesitate to ask any questions!

[elect]

I don't think so, but let me check

[Youssef Shoaib [MOD]]

What does your Value class look like btw?

[elect]

something like this:

class SliderRangeVars {
    inner class Value<N> where N : Number, N : Comparable<N> {
        lateinit var cur: N
        lateinit var min: N
        lateinit var max: N
        var resultFlags = 0
    }

    fun <N> values(): Array<Value<*>> = arrayOf(Value<Byte>(), Value<Ubyte>())
}

I also tried experimenting moving N on the outer class, but I get other problems later on..
I can add you to the repo, if you want

[Youssef Shoaib [MOD]]

I can't seem to define a Value<N> where N: Number without also adding the Comparable boundary. Please do add me to the repo and I'll tinker and see what I can do. My github is @kyay10