What information can serve as a key in a dictionary data structure?

In the data structure, a dictionary's key can be any data type that conforms to the Hashable protocol in Swift. This means the key must be unique and capable of computing a hash value for quick lookup.

Examples of keys:

• Strings (String)
• Integers (Int)
• Enumerations (enum) that conform to Hashable
• Tuples consisting of Hashable types

Example:

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

Here, the keys are strings.