What difficulties may arise when using the Hashable protocol in Swift?

Using the Hashable protocol in Swift can lead to the following challenges:

• Correct implementation of hash(into:): it is necessary to ensure that all properties involved in hash calculation are consistent with the Equatable implementation. Mismatch can cause errors when used in collections.
• Mutability of properties: if an object changes after its hash is computed, it will break the integrity of hash tables (e.g., dictionaries), as the hash will become invalid.
• Performance: hash calculation can be costly if the object contains a lot of data.

Example of correct implementation:

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

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

It is important that properties affecting equality are included in hash calculation.