i can not understand why 'selection' isn't recognised and the error isn't going away. please help.

//CODE SNIPPET:
//  VendingMachine.swift
//  VendingMachine
//
//  Created by Aananya on 05/03/17.
//  Copyright © 2017 Treehouse Island, Inc. All rights reserved.
//

import Foundation

enum VendingSelection {
    case soda
    case dietSoda
    case chips
    case cookie
    case sandwich
    case wrap
    case candyBar
    case popTart
    case water
    case fruitJuice
    case sportsDrink
    case gum
}

protocol VendingItem {
    var price : Double {get}
    var quantity: Int {get set}
}
protocol VendingMachine {
    var selection : [VendingSelection] {get}
    var inventory : [VendingSelection : VendingItem] {get set}
    var amountDeposited : Double {get set}

    init(inventory : [VendingSelection : VendingItem])
    func vend(_ quantity : Int , _ selection : VendingSelection) throws
    func deposit(_amount:Double)
}

struct Item {
    let price : Double
    var quantity : Int
}
enum InventoryError : Error {
case invalidResourse
case conversionFailure
case invalidSelection
}
class PlistConverter {
    static func dictionary (fromFile name : String , ofType type : String) throws -> [String : AnyObject]{
        guard let path = Bundle.main.path(forResource: name, ofType: type) else {
        throw InventoryError.invalidResourse
        }
        guard let dictionary = NSDictionary(contentsOfFile : path) as? [String:AnyObject]  else {
        throw InventoryError.conversionFailure
        }

    return dictionary
}


    class InventoryUnarchiver {
        static func vendingInventory (fromDictionary dictionary : [String:AnyObject]) throws -> [VendingSelection:VendingItem] {
            var inventory: [VendingSelection:VendingItem] = [:]
            for(key , value) in dictionary {
                if let itemDictionary = value as? [String:Any] ,
                    let price = itemDictionary ["price"] as? Double ,
                    let quantity = itemDictionary ["quantity"] as? Int {
                    let item = Item(price : price , quantity:quantity)
                    guard let selection = VendingSelection(rawValue : key) else {
                    throw InventoryError.invalidSelection}
                }
                inventory.updateValue(Item, forKey: selection)
            }
        }
    }

} ```