type myStr string

s := myStr("my string")

var x = map[int]string{
  3:         "oink",     // Valid, untyped numeric constant 3 is assignable to an int.
  int(4):    "quack",    // Valid, int(4) is of type int
  int64(12): "moo",      // Invalid, int64(12) is not converted to int
  8:         s,          // Invalid, type myStr is type string
  9:         string(s),  // Valid; explicit conversion to type string
}