What restrictions and requirements exist for objects to be used as elements of hash tables or hash structures in Swift?

In Swift, for an object to be used as an element of a hash table (for example, as a key in a dictionary or an element of a set), it must conform to the Hashable protocol.

Requirements:

• The object must implement the hash(into:) method, which combines property values to compute the hash code.
• The object must implement the equality operator == (the Equatable protocol) to compare elements correctly.

Example:

struct Person: Hashable {
    var id: Int
    var name: String

    func hash(into hasher: inout Hasher) {
        hasher.combine(id)
    }

    static func == (lhs: Person, rhs: Person) -> Bool {
        return lhs.id == rhs.id
    }
}

var peopleSet = Set<Person>()
peopleSet.insert(Person(id: 1, name: "Ivan"))

Thus, objects must have a stable and correctly implemented hash and comparison for proper operation in hash structures.