Pre-SIP: Bind variables for alternative patterns

[Sporarum]

I made a similar post not so long ago:

QoL: Sound binding in pattern alternatives

(This is about pattern alternatives, not union types !) enum Tree: case Wrap(t: Tree) case Node(t1: Tree, t2: Tree) case Leaf(value: Int) import Tree.* def rightmostValue(tree: Tree): Int = tree match case Wrap(subtree) | Node(_, subtree) => rightmostValue(subtree) case Leaf(value) => value The code above is unambiguous, right ? We extract a value subtree of type Tree, and recurse on it But this is not allowed: Illegal variable subtree in pattern alternative It is said as …

It looks into a lot of edge cases, like for example:

tree match
  case Wrap(subtree) | Leaf(subtree: Int) =>
    // What should be the type of subtree here ?