Swift: Comparing playing cards - Binary comparison cannot be applied

Question

I have the following code in Swift playground where a Card struct is created.

I need to compare cards to see what value is higher.

Ideally, I also need to check against all forms of binary operations <, >, <=, >=, etc

However, I keep getting an error that says:

error: binary operator '>' cannot be applied to two 'Card' operands if (ace > king) {
    ~~~ ^ ~~~~

A further message states:

note: overloads for '>' exist with these partially matching parameter lists: ((), ()), (UInt8, UInt8), (Int8, Int8), (UInt16, UInt16), (Int16, Int16), (UInt32, UInt32), (Int32, Int32), (UInt64, UInt64), (Int64, Int64), (UInt, UInt), (Int, Int), (UIContentSizeCategory, UIContentSizeCategory), (Date, Date), (IndexPath, IndexPath), (IndexSet.Index, IndexSet.Index), ((A, B), (A, B)), ((A, B, C), (A, B, C)), ((A, B, C, D), (A, B, C, D)), ((A, B, C, D, E), (A, B, C, D, E)), ((A, B, C, D, E, F), (A, B, C, D, E, F)), (Self, Other), (Self, R) if (ace > king) {

struct Card : Equatable {

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

    // Card properties and methods
    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
    }
}


extension Card {
    public static func == (lhs: Card, rhs: Card) -> Bool {
        return ((lhs.rank == rhs.rank) && (lhs.suit == rhs.suit))
    }
}

// Try to compare two cards
let ace = Card(rank: .ace, suit: .clubs)
let king = Card(rank: .king, suit: .diamonds)

if (ace > king) {
    print ("Ace is higher value")
}
else {
    print ("Ace is NOT higher")
}

I am wondering what I am getting wrong.

Answer 1

You need to conform to the Comparable protocol to be able to use the comparison operators (< and >).

extension Card: Comparable {
    static func < (lhs: Card, rhs: Card) -> Bool {
        return lhs.rank.values.first < rhs.rank.values.first
    }
}