Dictionary error: Ambiguous reference to member '+'

Question

I have the following code in a swift 3 method:

let dict = ["A": 1, "B": 2, "C": 3]
let sum = dict["A"]! + dict["B"]! + dict["C"]!

The code does not compile because of the Ambiguous reference to member '+' error. But if I try to add only two elements it compile and works as expected.

let dict = ["A": 1, "B": 2, "C": 3]
let sum = dict["A"]! + dict["B"]!

Works normally.

Am I missing something from how the language should work?

Answer 1

另一种解决方法：

let dict = ["A": 1, "B": 2, "C": 3]
let sum = 0 + dict["A"]! + dict["B"]! + dict["C"]!

Answer 2

您可以将dict["A"]与Int一起打包来解决错误。

这会将键“A”的值转换为Int，允许我们正确添加。

let dict = ["A": 1, "B": 2, "C": 3]
let sum = Int(dict["A"]!) + Int(dict["B"]!) + Int(dict["C"]!)

Answer 3

此代码已成功编译：

struct

我想，这个问题与复杂的表达有关。您可以阅读有关构建时间优化的更多信息in this article。

Answer 4

正如其他人评论的那样，这似乎是一个错误。但是，似乎你不太可能遇到这种情况，因为强行打开这样的字典元素是非常不安全的。这很好用：

let dict = ["A": 1, "B": 2, "C": 3]

if
  let a = dict["A"],
  let b = dict["B"],
  let c = dict["C"]
{
  let sum = a + b + c
}