Question

我需要任何 FileUpload项 Equatable 类中的容器（例如，从故事板初始化的UI类）。我需要这样的

Generic

但它不起作用，var items: [Equatable]?需要通用。存在普通Equatable类的问题。

好的 - 转到通用！但如果我这样做

Equatable

然后我将被迫在我的nonGeneric-UI类中指定类型。喜欢这个

class Item<Value: Equatable>: Equatable {
   var value: Value
   init(_ value: Value) {
       self.value = value
   }
   //Equatable
   public static func ==(lhs: Item, rhs: Item) -> Bool {
       return (lhs.value == rhs.value)
   }
}

但我们又遇到了一个问题，即没有共同的var items: [Item<WhatShouldBeHere?>]?类

All Equatable容器的任何解决方案？

Answer 1

代替存在类型，您需要使用类型橡皮擦：

public struct AnyEquatable: Equatable {
    public let value: Any
    private let equals: (Any) -> Bool

    public init<E: Equatable>(_ value: E) {
        self.value = value
        self.equals = { ($0 as? E) == value }
    }

    public static func == (lhs: AnyEquatable, rhs: AnyEquatable) -> Bool {
        return lhs.equals(rhs.value) || rhs.equals(lhs.value)
    }
}

示例用法：

let items = [
    AnyEquatable(1),
    AnyEquatable(1.23),
    AnyEquatable(true),
    AnyEquatable("some string")
]

let desired = "some string"
let desiredAsAnyEquatable = AnyEquatable(desired)
let desiredDescription = String(reflecting: desired)

for item in items {
    let itemDescription = String(reflecting: item.value)
    let isEqualToDesired = item == desiredAsAnyEquatable
    print("\(itemDescription) is \(isEqualToDesired ? "": "not ")equal to \(desiredDescription)")
}

示例输出：

1不等于“some string”

1.23不等于“some string”

true不等于“some string”

“some string”等于“some string”

Swift上的Common Equatable类

1 个答案: