Swift Dictionary With Expansive Type Constraints - swift

Question

I would like to define a dictionary that allows multiple specific types for values. I can currently define a dictionary like this:
var foo = [String: String]
which constrains the value to one specific type
OR
var foo = [String: AnyObject]
which constrains the value to AnyObject, which is not particularly constrained.
I'd like to do something like:
var foo = [String: <String, Int>]
which would allow me to insert only strings or ints as values in this dictionary.
I've considered the use of an enum as seen here: Generic dictionary value type in Swift but I would rather find a way that allows me to dynamically specify the types without expanding or creating a new enum.
var bar = [String: <String, Int, Bool, MyClass>]
It seems that I should be able to create a wrapper class with an internal dictionary of [String: AnyObject] that will allow for compile time type checking against an arbitrarily long list of classes that can be inserted.
class ECDictionary<T> {
private var internal_storage = [String: AnyObject]()
subscript(s: String) -> T {
get {
return internal_storage[s]
}
set(newValue) {
internal_storage[s] = newValue
}
}
}
var myECDictionary = ECDictionary<String, Int, OtherClass>()
I could build this with runtime type checking, but I'd rather it be enforced at compile time. Is this possible in any way?

Answer 1

If you want to a Dictionary where the value can be a String, an Int, a Bool or a MyClass you should
Define your protocol
protocol MyDictionaryValue { }
Conform String, Int, Bool and MyClass to MyDictionaryValue
extension String: MyDictionaryValue { }
extension Int: MyDictionaryValue { }
extension Bool: MyDictionaryValue { }
extension MyClass: MyDictionaryValue { }
Declare your dictionary
var dict = [String:MyDictionaryValue]()
Usage
dict["a"] = "a string"
dict["b"] = 1
dict["c"] = true
dict["d"] = MyClass()
dict["e"] = CGPointZero // error
dict["f"] = UIView() // error