ios - 如何获取泛型类型类的大小(计数)？

Question

我如何创建一个通用类，无论它是 Int、String 等，我都可以在其中获取项目的大小(或计数)...

class Node<T: Equatable> {

    var item: T? = nil
    var next: Node? = nil

    init(item:T, node:Node?) {
        self.item = item
        self.next = node
    }

    var count:Int { <-------------- this is what I need to fix
        return item.count
    }

}

我想这样做，这样我就可以像这样比较项目:

let one = Node<Int>(item:1, node:nil)
let two = Node<Int>(item:2, node:nil)

return one.count < two.count <--------- should return true

let str1 = Node<String>(item:"moose", node:nil)
let str2 = Node<String>(item:"cow", node:nil)

return str1.count < str2.count <------- should return false

更新 我现在遇到了正常比较的问题。我收到错误消息，“二元运算符‘==’不能应用于‘Any’和‘Any?’类型的操作数。” (又名“协议(protocol) <>”)”

func search(item:Any) -> Bool {

    var current:Node? = self.head
    var found = false

    while current != nil && found != true {
        if current?.item == item { <---------this is the error line
            found = true
        } else {
            current = current?.next
        }
    }

    return found
}

除了用于节点比较的运算符之外，我还尝试实现一个自定义的“==”运算符

func ==(lhs: Node, rhs: Node) -> Bool {
    return lhs.count == rhs.count
}

func ==(lhs: Any, rhs: Any) -> Bool {
    return lhs == rhs
}

Answer 1

您只需要使您的 Node 类符合 Equatable 和 Comparable，并将您的项目类型更改为 Any?:

class Node: Equatable, Comparable {

    var item: Any? = nil
    var next: Node? = nil

    init(item: Any?, node: Node?) {
        self.item = item
        self.next = node
    }
    var count: Int {
        // the trick is here, just conditionally casting to Int or String and return its Int value or the string characters count.
        if let val = item as? Int {
            return val
        }
        if let str = item as? String {
            return str.characters.count
        }
        return 0
    }
}

---

func ==(lhs: Node, rhs: Node) -> Bool {
    return lhs.count == rhs.count
}

func <(lhs: Node, rhs: Node) -> Bool {
    return lhs.count < rhs.count
}

---

用法:

let nodeOne = Node(item:1, node:nil)
let nodeTwo = Node(item:2, node:nil)

 print(nodeOne < nodeTwo) // true

let nodeStr1 = Node(item:"moose", node:nil)
let nodeStr2 = Node(item:"cow", node:nil)

print( nodeStr1 < nodeStr2)  //  false