Swift implementation of an ordered Dictionary

OrderedDictionary

import Foundation

struct OrderedDictionary<KeyType:Hashable, ValueType:Hashable>{
    var keyArray = [KeyType]()
    var keyToValue = [KeyType:ValueType]()
    
    subscript(key:KeyType) -> ValueType? {
        get{
            return keyToValue[key]
        }
        set{
            let existingValue = keyToValue[key]
            keyToValue[key] = newValue
            if existingValue == nil {
                keyArray.append(key)
            }
        }
    }
    
    subscript(value:Int) -> (KeyType,ValueType?) {
        get{
            let key = keyArray[value]
            return (key,keyToValue[key])
        }
    }
}