如何根据 class 中的另一个属性创建变量属性

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

以上代码在playground中没有错误。但是，如果我不知道餐厅总数是 21 家（可能有数百家，我不想数）怎么办？我尝试了以下代码来创建一个不可变的计算属性。但它不会工作，因为稍后属性将被函数 setTheVisitedRestaurants 更改并且它将 return 出错。

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

一句话，问题就是如何根据class中的另一个属性创建一个变量属性。我是初学者，我真的尝试过。请帮忙！

Answer 1

使用 lazy 关键字声明 restaurantIsVisited。这将确保它在第一次访问之前不会被创建，到那时你将能够向 restaurantNames 请求它的 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

为什么不用结构体来表示餐厅，例如：

struct Restaurant {
    let name: String
    var visited: Bool

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

现在可以更轻松地跟踪去过哪些餐厅，哪些没有去过，因为您不必担心每家餐厅的信息会被分成两个数组。

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

用法：

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

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