program()
type
  File = record
    fd: Int
  end

  Map#[K, V] = record
    key: ^K;
    value: ^V
  end

  Cache#[K, V] = record(Map#[Word8, V])
    newest: ^K
  end

var
  store: Cache#[Int, File]
  byte_key: ^Word8
  upcast: ^Map#[Word8, File]

proc put#[K2, V2](target: ^Map#[K2, V2]; key: ^K2)
begin
  target^.key := key
return

begin
  upcast := @store;
  put(@store, byte_key)
end.