为啥这个元组在 swift 3 中没有更多上下文就模棱两可？

Posted 2023-03-12

【中文标题】为啥这个元组在 swift 3 中没有更多上下文就模棱两可？

【英文标题】：Why is this tuple ambiguous without more context in swift 3?为什么这个元组在 swift 3 中没有更多上下文就模棱两可？

【发布时间】：2016-06-24 19:07:50

【问题描述】：

在查看了几个月前有效的代码后，能否解释一下如何修复此错误？显示的错误是“表达式类型不明确，没有更多上下文”。

var products = [("Kayak","A boat for one person","Watersports",275.0,10),
                ("Lifejacket","Protective and fashionable","Watersports",48.95,14),
                ("Soccer Ball","FIFA-approved size and weight","Soccer",19.5,32),
                ("Corner Flags","Give your playing field a professional touch","Soccer",34.95,1),
                ("Stadium","Flat-packed 35,000-seat stadium","Soccer",79500.0,4),
                ("Improve your brain efficiency by 75%","Chess",16.0,8),
                ("Unsteady Chair","Secretly give your opponent a disadvantage","Chess",29.95,3),
                ("Human Chess Board","A fun game for the family","Chess",75.0,2),
                ("Bling-Bling King","Gold-plated,diamon-studded King","Chess",1200.0,4)]

【问题讨论】：

查找“奇怪错误信息”原因的常用程序是删除行直到问题消失，然后重新添加行，以隔离问题。你可以自己轻松地做到这一点......

当内置类型推断失败时，我更喜欢明确说明类型并查看错误是否消失。如果不是，则很好地证明该类型实际上并不模棱两可，而是完全错误（或者至少不是您认为的那样）。

善待你的编译器。不要在不告诉它类型的情况下给它很大的初始值：var products: [(String, String, String, Double, Int)] = [...。如果你这样做了，它会告诉你error: cannot convert value of type '(String, String, Double, Int)' to expected element type '(String, String, String, Double, Int)' 并指出问题所在。

【参考方案1】：

这一行：

("Improve your brain efficiency by 75%","Chess",16.0,8),

只有 2 个字符串而不是 3 个。活动名称 (?) 似乎丢失了。

【参考方案2】：

不要像这样滥用结构。您应该将其重构为结构：

struct Product  //fill these names in better
    let name: String
    let description: String
    let category: String
    let price: Double
    let x: Int


var products = [
    Product(name: "Kayak",
        description: "A boat for one person",
        category: "Watersports", price: 275.0, x: 10),
    Product(name: "Lifejacket",
        description: "Protective and fashionable",
        category: "Watersports", price: 48.95, x: 14),
    Product(name: "Soccer Ball",
        description: "FIFA-approved size and weight",
        category: "Soccer", price: 19.5, x: 32),
    Product(name: "Corner Flags",
        description: "Give your playing field a professional touch",
        category: "Soccer", price: 34.95, x: 1),
    Product(name: "Stadium",
        description: "Flat-packed 35,000-seat stadium",
        category: "Soccer", price: 79500.0, x: 4),
    Product(name: "YOU FORGOT TO GIVE ME A NAME",
        description: "Improve your brain efficiency by 75%",
        category: "Chess", price: 16.0, x: 8),
    Product(name: "Unsteady Chair",
        description: "Secretly give your opponent a disadvantage",
        category: "Chess", price: 29.95, x: 3),
    Product(name: "Human Chess Board",
        description: "A fun game for the family",
        category: "Chess", price: 75.0, x: 2),
    Product(name: "Bling-Bling King",
        description: "Gold-plated,diamon-studded King",
        category: "Chess", price: 1200.0, x: 4)
]

这使得所有这些值的含义更加清晰，并且使访问它们更加自然（例如，您可以通过product.name 而不是product.1 获取名称）。