Tuple “upcasting” in Swift

Question

If I have a tuple with signature (String, Bool) I cannot cast it to (String, Any). The compiler says:

error: cannot express

Answer 1

The Swift compiler will enforce that you are explicit about your types. So if you declare it as (String, Bool) it will not allow the conversion.

The following works as expected in Playground:

var specificTuple : (String, Bool) = ("Hi", false)
var generalTuple  : (Any, Any)     = ("Hi", false)

var gany = generalTuple
gany.1 = "there"
gany                           // (.0 "Hi", .1 "there")

var spany = specificTuple
spany.1 = "there"             // error

You can create the (Any, Any) tuple ad hoc but you will need to decompose it

var any : (Any, Any)  = (specificTuple.0, specificTuple.1)
any.1 = "there"
any                          // (.0 "Hi", .1 "there")