不能下标'inout'类型的值[String：Double]（又名inout Dictionary< String，Double>） [英] cannot subscript a value of type 'inout' [String :Double] (aka inout Dictionary<String, Double>)

问题描述

如果我尝试在字典中添加三个菜单，那么当我尝试强制打开菜单中的第三个项目时，我不会让我发生错误。但是如果我强制解开其中两个，我可以得到他们的两个总和

How can if i try to add three menus in the dictionary i wont let me and throws an error when i try to force unwrap the 3rd item in the menu. However if i force unwrap two of them, i can get them sum of two

var menu = ["fish": 10.99, "chips": 5.99, "kebab": 6.99]
var totalCost = menu["fish"]! + menu["chips"]! + menu["kebab"]!
print("The total cost of the three items is \(totalCost)")

但是当我以这种方式尝试使用它的时候

But when i tried it this way it worked

var menu = ["fish": 10.99, "chips": 5.99, "kebab": 6.99]
var totalCost = menu["fish"]! + menu["chips"]! 
var thisCost = totalCost + menu["kebab"]!
print("The total cost of the three items is \(thisCost)"

我正在使用swift 3.是否可以在swift 3中不再支持？

I am using swift 3. Could it be that can no longer be supported in swift 3?

推荐答案

你可以一直遍历，添加到总计，更简单的一行长的添加。

You can alway iterate through and add to total, much simpler that a line of long addition.

var totalCost: Double = 0
for each in menu {
    totalCost += each.value
}
print(totalCost)

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