public protocol Primitive {}

extension String: Primitive {}
extension Int: Primitive {}
extension Double: Primitive {}
extension Float: Primitive {}
extension Bool: Primitive {}
extension Array: Primitive where Element: Primitive {}
extension Dictionary: Primitive where Key == String, Value: Primitive {}

public protocol UserInfoable {
    /// Dictionary for keeping information for the implementing object using only Primitives.
    var userInfo: [String: Primitive] { get set }
}