How to create an variable property based on the other property in the class

Question

class someClass
{
// This is a list of restaurant names
var restaurantNames = ["Cafe Deadend", "Homei", "Teakha", "Cafe Loisl", "Petite Oyster", "For Kee Restaurant", "Po's Atelier", "Bourke Street Bakery", "Haigh's Chocolate", "Palomino Espresso", "Upstate", "Traif", "Graham Avenue Meats", "Waffle & Wolf", "Five Leaves", "Cafe Lore", "Confessional", "Barrafina", "Donostia", "Royal Oak", "Thai Cafe"]

// This is an array to record the restaurants I have visited 
var restaurantIsVisited:[Bool] = [Bool](count: 21, repeatedValue: false)

// This is a function to set the restaurants I have visited
func setTheVisitedRestaurants(somenumber:Int)
{
self.restaurantIsVisited[somenumber] = true
}

}
let thisVisit = someClass()
thisVisit.setTheVisitedRestaurants(1)
let somearray = thisVisit.restaurantIsVisited

Above code has no error in playground. But what if I don't know the number of the total restaurants is 21 (It could be hundreds and I don't want to count). I tried the following code to create an immutable computed property. But it won't work because later on the property will be changed by function setTheVisitedRestaurants and it will return an error.

// var restaurantIsVisited:[Bool]{
//        return [Bool](count: restaurantNames.count, repeatedValue: false)
//    }

In a word, the question is like how to create an variable property based on the other property in the class. I am a beginner and I really tried. Please help!

Answer 1

Declare restaurantIsVisited with the lazy keyword. This will insure that it isn't created until it is accessed the first time, and by that time you will be able to ask restaurantNames for its count:

class someClass
{
    // This is a list of restaurant names
    var restaurantNames = ["Cafe Deadend", "Homei", "Teakha", "Cafe Loisl", "Petite Oyster", "For Kee Restaurant", "Po's Atelier", "Bourke Street Bakery", "Haigh's Chocolate", "Palomino Espresso", "Upstate", "Traif", "Graham Avenue Meats", "Waffle & Wolf", "Five Leaves", "Cafe Lore", "Confessional", "Barrafina", "Donostia", "Royal Oak", "Thai Cafe"]

    // This is an array to record the restaurants I have visited
    lazy var restaurantIsVisited:[Bool] = [Bool](count: self.restaurantNames.count, repeatedValue: false)

    // This is a function to set the restaurants I have visited
    func setTheVisitedRestaurants(somenumber:Int)
    {
        self.restaurantIsVisited[somenumber] = true
    }

}

let thisVisit = someClass()
thisVisit.setTheVisitedRestaurants(1)
let somearray = thisVisit.restaurantIsVisited
println(somearray.count)  // "21"

Answer 2

Why not use a struct to represent a restaurant, for example:

struct Restaurant {
    let name: String
    var visited: Bool

    init(name: String, visited: Bool = false) {
        self.name = name
        self.visited = visited
    }
}

Now it's much easier to keep track of which restaurants have been visited and which ones haven't because you haven't got to worry about information on each restaurant being separated into two arrays.

struct SomeStruct {
    var restaurants = [Restaurant(name: "Cafe Deadend"), 
                       Restaurant(name: "Homei"),
                       Restaurant(name: "Cafe Loisl")]
}

Usage:

var thisVisit = SomeStruct()
thisVisit.restaurants[0].visited = true