Nested types

Enumerations are often created to support a specific class or structure's functionality. Likewise, it can be convenient to declare utility classes and structures purely to use within the context of a complex type.

Swift enables us to declare nested types, whereby we nest supporting enumerations, classes, and structures within the definition of the type that they support. The following example, borrowed from The Swift Programming Language by Apple Inc., presents nested types:

struct BlackjackCard { 
    // nested Suit enumeration 
    enum Suit: Character { 
        case spades = "♠", 
        hearts = "♡", 
        diamonds = "♢", 
        clubs = "♣" 
    } 

    // nested Rank enumeration 
    enum Rank: Int { 
        case two = 2, three, four, five, six, seven, eight, nine, ten 
        case jack, queen, king, ace 

        // nested struct 
        struct Values { 
            let first: Int, second: Int? 
        } 

        var values: Values { 
            switch self { 
            case .ace: 
                return Values(first: 1, second: 11) 
            case .jack, .queen, .king: 
                return Values(first: 10, second: nil) 
            default: 
                return Values(first: self.rawValue, second: nil) 
            } 
        } 
    } 

    let rank: Rank, suit: Suit 

    var description: String { 
        var output = "suit is \(suit.rawValue)," 
        output += "value is \(rank.values.first)" 
        if let second = rank.values.second { 
            output += " or \(second)" 
        } 
        return output 
    } 
}