不能下标类型为“inout"的值 [String :Double](又名 inout Dictionary<String, Double>) [英] cannot subscript a value of type &#39;inout&#39; [String :Double] (aka inout Dictionary&lt;String, Double&gt;)

问题描述

如果我尝试在字典中添加三个菜单，当我尝试强制解开菜单中的第三个项目时，我不会允许并抛出错误，该怎么办.但是，如果我强制打开其中的两个，我可以得到它们的总和

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它时它起作用了

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.难道 swift 3 不再支持它了吗?

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

推荐答案

你总是可以迭代并添加到总数中，比一行长的添加要简单得多.

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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