Sould infix work on enum?

[nicolasstucki]

Compiler version

3.3

Minimized example

import language.future
enum Extends[A, B]:
  case Ev[B, A <: B]() extends (A Extends B)

3 |  case Ev[B, A <: B]() extends (A Extends B)
  |                                  ^^^^^^^
  |Alphanumeric type Extends is not declared infix; it should not be used as infix operator.
  |Instead, use prefix syntax Extends[...] or backticked identifier `Extends`.
  |The latter can be rewritten automatically under -rewrite -source future-migration.

but

infix enum Extends[A, B]:
  case Ev[B, A <: B]() extends (A Extends B)

1 |infix enum Extends[A, B]:
  |           ^^^^^^^
  |           Only access modifiers are allowed on enum definitions

Question

Should infix work on enum to mark it as an infix type?

[nicolasstucki]

Example from https://github.com/lampepfl/dotty/blob/main/tests/pos/i7424c.scala

[nicolasstucki]

I assume it should be allowed. @odersky is this the case?

[odersky]

I think we should allow it.

[bishabosha]

doesn't this need a SIP?

[sjrd]

I don't think so. It looks to me light an oversight of the implementation. It's not like when we examined infix in SIP-2->3 that we said "let's add infix and allow to put on type definitions except enums".

[bishabosha]

the linked PR #19010 doesnt enable this, but should we also allow infix enum cases?

e.g.

import Expr.*

enum Expr[+A]:
  infix case to[A <: Int, B <: Int](min: A, max: B) extends Expr[Range]

extension [A <: Int](min: A)
  infix def to[B <: Int](max: B): A to B = Expr.to(min, max)

val foos: 1 to 23 = 1 to 23

[sjrd]

They declare class types, so IMO yes.

[odersky]

Some enum cases declare class types, but not all. So we'd have to restrict it to those cases that actually do declare class types.