What steps are necessary to use a complex structure as a key in a dictionary?

To use a complex structure (for example, a custom class or struct) as a key in a dictionary in Swift, this type must conform to the Hashable protocol. This means that the struct must have a properly implemented hash calculation method and equality comparison.

Example:

struct Person: Hashable {
    let firstName: String
    let lastName: String

    // The compiler will automatically generate hash(into:) and == if all properties are Hashable
}

var dict: [Person: String] = [:]
dict[Person(firstName: "Ivan", lastName: "Ivanov")] = "Sample value"

If the struct contains properties that do not conform to Hashable, you need to manually implement the hash(into:) and == methods.

Thus, the steps are:

1. Ensure all properties of the struct conform to Hashable.
2. Make the struct or class conform to the Hashable protocol.
3. Use this struct as a key in the dictionary.