read_subtyping_problem.pony

use "collections"

actor Main
  let m1: Map[String, String] = Map[String, String]
  let m2: Map[String, Array[String]] = Map[String, Array[String]]

  // works fine
  fun getThingsStringLiteral(): String =>
    m1.get_or_else("foo", "")

  // works fine
  fun getThingsStringRefRecovered(): String =>
    m1.get_or_else("foo", recover val String end)
  
  // Array[String val] ref is not a subtype of Array[String val] #read: ref is not a subtype of #read
  fun getThingsStringArrayLiteral(): Array[String] =>
    m2.get_or_else("foo", [""])

  // Array[String val] val is not a subtype of Array[String val] #read: val is not a subtype of #read
  fun getThingsStringArrayRefRecovered(): Array[String] =>
    m2.get_or_else("foo", recover val Array[String] end)

There's some problems lurking in here...

  fun getThingsStringArrayRefRecovered(): Array[String] =>
    m2.get_or_else("foo", recover val Array[String] end)

So m2 will return a Array[String] ref however your else is Array[String] val.
That would be a problem.

I think you wanted something more like...

fun getThingsStringArrayRefRecovered(): this->Array[String] =>
m2.get_or_else("1", recover Array[String] end)