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Implement tracked members #21754

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KacperFKorban opened this issue Oct 11, 2024 · 0 comments · Fixed by #21761
Closed

Implement tracked members #21754

KacperFKorban opened this issue Oct 11, 2024 · 0 comments · Fixed by #21761
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@KacperFKorban
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area:experimental:modularity Issues related to the modularity extension. itype:enhancement

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@KacperFKorban
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It would be great to be able to declare abstract tracked members.

tracked members, when overridden, will keep their exact type.

e.g. the following code should compile

import scala.language.experimental.modularity
import scala.language.future

trait F:
  tracked val x: Int

object Test:
  val f = new F:
    val x = 1

  summon[f.x.type <:< 1]
@KacperFKorban KacperFKorban added itype:enhancement area:experimental:modularity Issues related to the modularity extension. labels Oct 11, 2024
@KacperFKorban KacperFKorban self-assigned this Oct 11, 2024
@KacperFKorban KacperFKorban mentioned this issue Oct 14, 2024
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KacperFKorban added a commit that referenced this issue Dec 19, 2024
@KacperFKorban @mbovel @odersky
Implement tracked members (#21761)
0041987 
closes #21754 

Allow for the `tracked` modifier to be used for `val` members of classes
and traits. `tracked` members and members inheriting from `tracked`
force the type of the member (or it's overriding member) to be as exact
as
possible. More precisely, it will will assign the `tracked` member the
infered type of the rhs. For instance, consider the following
definition:

```scala 3
trait F:
  tracked val a: Int
  tracked val b: Int

class N extends F:
  val a = 22 // a.type =:= 22
  val b: Int = 22 // b.type =:= Int
  tracked val c = 22 // c.type =:= 22
```

Here, the `tracked` modifier ensures that the type of `a` in `N` is `22`
and not `Int`. But the type of `b` is `N` is `Int` since it's explicitly
declared as `Int`. `tracked` members can also be immediately
initialized, as in the case of `c`.

---------

Co-authored-by: Matt Bovel <[email protected]>
Co-authored-by: odersky <[email protected]>
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Implement tracked members dotty-staging/dotty
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