Argument type 'VendingItem' does not conform to expected type 'itemType'

protocol VendingMachineType {
    var selection: [VendingSelection] { get } //Read only b/c you only have a set selection
    var inventory: [VendingSelection: ItemType]  { get set } //Inventory changes, must be get/set
    var amountDeposited: Double { get set }

    init(inventory: [VendingSelection: ItemType])
    func vend(selection: VendingSelection, quantity: Double) throws
    func deposit(amount: Double)
}

let item = VendingItem(price: price, quantity: quantity)

import Foundation

//Protocols

protocol VendingMachineType {
    var selection: [VendingSelection] { get } //Read only b/c you only have a set selection
    var inventory: [VendingSelection: ItemType]  { get set } //Inventory changes, must be get/set
    var amountDeposited: Double { get set }

    init(inventory: [VendingSelection: ItemType])
    func vend(selection: VendingSelection, quantity: Double) throws
    func deposit(amount: Double)
}

protocol ItemType {
    var price: Double { get }
    var quantity: Double { get set }
}

//Error Types
enum InventoryError: ErrorType {
    case invalidResource
    case conversionError
    case invalidKey
}


//HELPER Classes
class PListConverter {
    class func dictionaryFromFile(resource: String, ofType type: String) throws -> [String: AnyObject] {
        //resource is resource location. type is resource type

        guard let path = NSBundle.mainBundle().pathForResource(resource, ofType: type) else {
            //Stuff in here runs if it returns null
            throw InventoryError.invalidResource
        }

        guard let dictionary = NSDictionary(contentsOfFile: path), let castDictionary = dictionary as? [String: AnyObject] else {
            throw InventoryError.conversionError
        }

        return castDictionary
    }
}

class InventoryUnarchiver {
    class func vendingInventoryFromDictionary(dictionary: [String: AnyObject]) throws -> [VendingSelection : ItemType] {
        //Return type is specified as a protocol so  we MUST return "[VendingSelection : ItemType]"
        var inventory: [VendingSelection : ItemType] = [:] //Creates empty variable dictionary

        for (key, value) in dictionary {
            if let itemDict = value as? [String : Double],
                let price = itemDict["price"],
                let quantity = itemDict["quantity"]{
                //Second two let statements check to see if exists an itemDict key with string price and quantity (unwrapping optionals)
                let item = VendingItem(price: price, quantity: quantity)

                //Now we have price and quantity of type double. key as type string and value of type anyObject. We need to update the value of the inventory dictionary but to updateValue, we need key to be of type VendingSelection.
                //VendingSelection is an enum with a raw value of String
                //So, if we assign key to VendingSelection(rawValue: key) and the key string matches a VendingSelection case then key becomes of type VendingSelection
                guard let key = VendingSelection(rawValue: key) else {
                    //Means key does not match with enum case (THROW ERROR)
                    throw InventoryError.invalidKey
                }//Checks to see if key(String) matches a case of VendingSelection. If so key(String) becomes key(VendingSelection: matchingCase)
                inventory.updateValue(item, forKey: key)
            }
        }
    return inventory
    }
}

//CONCRETE TYPES

//Enums
enum VendingSelection: String {
    case Soda
    case DietSoda
    case Chips
    case Cookie
    case Sandwich
    case Wrap
    case CandyBar
    case PopTart
    case Water
    case FruitJuice
    case SportsDrink
    case Gum
}

struct VendingItem {
    //Value types (structs/enums) ARE THINGS
    //refrence types (protocols) DO THINGS
    let price: Double
    var quantity: Double
}

class VendingMachine: VendingMachineType {
    //Classes are good at modeling state, inventory can change
    let selection: [VendingSelection] = [.Soda, .DietSoda, .Chips, .Cookie, .Sandwich, .Wrap, .CandyBar, .PopTart, .Water, .FruitJuice, .SportsDrink, .Gum]
    var inventory: [VendingSelection : ItemType]
    var amountDeposited: Double = 10.0

    required init(inventory: [VendingSelection: ItemType]) {
        self.inventory = inventory
    }

    func vend(selection: VendingSelection, quantity: Double) throws {
        //add code
    }

    func deposit(amount: Double) {
        //add code
    }

}