How to create an Array or Dictionary whose values can only be String, Int and Boolean? [duplicate]

Answer 1

protocol Elem {} 
extension Int: Elem {}  
extension String: Elem {} 
extension Bool: Elem {} 
let arr = [Elem]()

Answer 2

You can do it by declaring a dummy protocol

protocol SpecialType {}

and let conform the requested types to that protocol

extension String : SpecialType{}
extension Int : SpecialType{}
extension Bool : SpecialType{}

Now the compiler complains if you try to add a Double

let specialDict : [String:SpecialType] = ["1" : "Hello", "2": true, "3": 2.0]
// value of type 'Double' does not conform to expected dictionary value type 'SpecialType'