Match Type documentation example does not compile

[joshlemer]

The following example from the dotty website does not compile:

http://dotty.epfl.ch/docs/reference/match-types.html
EDIT: new location of docs are here https://dotty.epfl.ch/docs/reference/new-types/match-types.html

scala>    type LeafElem[X] = X match {                                                                                                                                                                                                        
     |     case String => Char
     |     case Array[t] => LeafElem[t]
     |     case Iterable[t] => LeafElem[t]
     |     case t <: AnyVal => t
     |   }
5 |    case t <: AnyVal => t
  |           ^^
  |           '=>' expected, but '<:' found

[milessabin]

This can be rewritten as,

type LeafElem[X] = X match {
  case String => Char
  case Array[t] => LeafElem[t]
  case Iterable[t] => LeafElem[t]
  case AnyVal => X
}

which works as expected.

It appears that having a variable in the outermost position of a type pattern isn't currently supported. Neither is the use of bound syntax in that context either.

[milessabin]

Another working rewrite,

type AV[t <: AnyVal] = t

type LeafElem[X] = X match {
  case String => Char
  case Array[t] => LeafElem[t]
  case Iterable[t] => LeafElem[t]
  case AV[t] => t
}

[biboudis]

Should we update the documentation and close the issue or leave it for now? @odersky WDYT?

[milessabin]

The example should work.