What can be the key and value for a dictionary?

In iOS (Swift), a dictionary (Dictionary) is a collection of key-value pairs.

• Key can be any type that conforms to the Hashable protocol. This means the key must be hashable for quick lookup. For example, String, Int, UUID, and other standard types.

• Value can be any type, including structures, classes, primitives, or even other collections.

Example:

var dict: [String: Int] = ["apple": 3, "banana": 5]

// Key — String (hashable), value — Int

// You can also use custom types if they conform to Hashable:
struct User: Hashable {
    let id: Int
    let name: String
}

var userScores: [User: Double] = [:]

It is important that keys are immutable and hashable so that the dictionary can function correctly.