ios - 具有不同属性的两个对象的哈希值相同

Question

考虑这个结构

struct Node : Hashable {
 let value : Int
 let i : Int
 let j : Int

 init(withValue val : Int, position : (Int,Int)){
    value = val
    self.i = position.0
    self.j = position.1
 }

 var hashValue: Int {
    return "\(value),\(i),\(j)".hashValue
 }
}

我的== 运算符

func ==(left: Node, right: Node) -> Bool {
    return left.hashValue == right.hashValue
}

当我创建 2 个节点时:

let node1 = Node(withValue: 1260, position: (8,694))
let node2 = Node(withValue: 33, position: (257,286))

比较它们:

   node1 == node2   //true ???

为什么 hashValue 函数没有按预期工作？

是否应该以其他方式实现？

反问:如果是，计算这种对象的 hashValue 的正确方法是什么？

更多信息

当我调试这个时:

(lldb) po node1.hashValue
4799450060528192039

(lldb) po node2.hashValue
4799450060528192039

Answer 1

相等的散列值不保证相等的原始值。整体概念hash collisions存在就是因为这个原因:

In computer science, a collision or clash is a situation that occurs when two distinct pieces of data have the same hash value...

Collisions are unavoidable whenever members of a very large set (such as all possible person names, or all possible computer files) are mapped to a relatively short bit string.

这意味着这个==操作符的实现是错误的:

func ==(left: Node, right: Node) -> Bool {
    return left.hashValue == right.hashValue
}

应该是:

func ==(left: Node, right: Node) -> Bool {
   return left.value == right.value
       && left.i == right.i
       && left.j == right.j
}