Hi , is it possible to build a `inline class` pool...

# language-proposals

[smallufo]

Hi , is it possible to build a inline class pool that returns same reference ?
Related link : https://kotlinlang.slack.com/archives/C0B8Q383C/p1644805562640269

Play ground : https://pl.kotl.in/uBVYwgQgO?theme=darcula

I am building a carousel-like Int , naming Three , which restrict any Int value to 1..3 . That is Three.of(1) == Three.of(4) ,  Three.of(0) == Three.of(3)   . I use a prebuild  array to simulate caching , hoping they get the same reference

private val array by lazy {
  arrayOf(Three(1), Three(2), Three(3))
}

But it seems it doesn't work. When comparing reference === , it complains Identity equality for arguments of types Three and Three is forbidden , which is counter-intuitive .

[Roukanken]

Why?

This goes against very idea of value classes - value's class value is it's identity. If two values are equal, they are identical.

When you declare class a value class, you are basically saying "Okay, this class has no identity beyond the data it holds", an identity operator on it doesn't make sense - if it existed, it would do exactly same thing as equals operator

[Roukanken]

That's from theory standpoint, from more practical one:

Value (or Inline) classes can be inlined as compiler wishes. Now if you have an inlined x: Int and not inlined y: Three how would you compare they have same identity (when original code had x === y ?)

You can't - the only reason the inlining can be consistent is that this operation is invalid. Equals operator is easy to do: x == y in original code would just turn to x == y.value in inlined one.

[Youssef Shoaib [MOD]]

For your Three class btw, it's probably best to use an enum instead with 3 values

[smallufo]

It makes sense , thanks