arrays - 如何快速调用或访问结构计算变量？

Question

struct Item {
    var iQuantity : Int
    var iPrice : Int
    var iCost : Int { return iQuantity*iPrice }
}

let item1 = Item(iQuantity: 1, iPrice: 20)
let item2 = Item(iQuantity: 3, iPrice: 30)

let myDict = ["dog": item1, "cat": item2]

Array(myDict.values   // only have price / quantity
Array(myDict.iCost)  // want something like this not working

---

// want array of all cost( P*Q )  for each item => [20,90] 

Answer 1

试试这个。

struct Item {
    var iQuantity : Int
    var iPrice : Int
    var iCost : Int { return iQuantity*iPrice }
}

let item1 = Item(iQuantity: 1, iPrice: 20)
let item2 = Item(iQuantity: 3, iPrice: 30)

let myDict = ["dog": item1, "cat": item2]

let myCosts = myDict.map( { $0.1.iCost } ) // [90, 20]

正如评论员@konrad.bajtyngier 所说，您的myDict 是一本字典。当然，这意味着项目的顺序是未定义的，这可能不是您所期望的。您可能希望将您的数据结构重新定义如下:

struct Item {
    var iName: String
    var iQuantity : Int
    var iPrice : Int
    var iCost : Int { return iQuantity*iPrice }
}

let item1 = Item(iName: "Dog", iQuantity: 1, iPrice: 20)
let item2 = Item(iName: "Cat", iQuantity: 3, iPrice: 30)

let myArray = [item1, item2]

let myCosts = myArray.map( { $0.iCost } ) // [20, 90]