swift - 嵌套数组 - 不明确

Question

尝试创建下面的数组时，出现以下错误:

type of expression is ambiguous without more context

在 Swift 中可以使用这样的数组吗？如果是，它是如何声明的？

var jobArray = [
    ["Dog Walker", "Job Description", ["Monday", "Wednesday", "Friday"], "7"],
    ["Babysitter", "Job Description", ["Tuesday", "Wednesday"], "15"],
    ["Leaves Raker", "Job Description", ["Sunday", ""], "10"]
]

Answer 1

我猜你在 playground 中没有导入 Foundation 或类似的东西:

// uncommenting the below line fixes the problem
// import Foundation

// with it commented out, 
var jobArray = [
    ["Dog Walker", "Job Description", ["Monday", "Wednesday", "Friday"], "7"],
    ["Babysitter", "Job Description", ["Tuesday", "Wednesday"], "15"],
    ["Leaves Raker", "Job Description", ["Sunday", ""], "10"]
]

没有它你会得到两个错误:

error: '_' is not convertible to 'StringLiteralConvertible'
["Dog Walker", "Job Description", ["Monday", "Wednesday", "Friday"], "7"],
               ^~~~~~~~~~~~~~~~~
error: type of expression is ambiguous without more context

第一个更重要。第二个是Swift上去回家的神器。

为什么？因为 [jobArray] 的类型是什么？ Swift 标准库中没有符合此定义的类型——您需要一个 [[Something]]，其中 Something 符合 StringLiteralConvertible(对于 "Dog Walker")和 ArrayLiteralConvertible(对于 ["Sunday", ""])。没有一个。

可悲的是，恕我直言，非常可悲的是，这样的事情是在 Foundation 中定义的。这就是为什么它会在您添加导入时进行编译。

我强烈建议，不要像这样定义这个数组，而是实现一个简单的 struct:

struct Job {
    let jobDescription: String
    let days: [String]  // or even an enum for the days of the week
    let hourlyPay: Double
}

var jobArray = [
    Job(jobDescription: "Dog Walker", days:  ["Monday", "Wednesday", "Friday"], hourlyPay: 7),
    Job(jobDescription: "Babysitter", days:  ["Tuesday", "Wednesday"], hourlyPay: 15),
    // etc
]