Using associatedtype in a delegate protocol for a generic type

I have a Game class. I made it generic because I was need to support different types of boards. Now I just want to add a classical iOS-style delegate with a method which will take a game and a new points value as parameters. How to achieve this in the Swift associatedtype way? I really confused that I can't impelemnt such simple logic.

protocol GamePointsDelegate {
    associatedtype B: Board
    func game(_ game: Game<B>, didSetPoints points: Int)
}

class Game<B: Board> {
    let board: Board

    var points = 0 {
        // Compiler Error
        // Member 'game' cannot be used on value of protocol type 'GamePointsDelegate'; use a generic constraint instead
        didSet { pointsDelegate?.game(self, didSetPoints: points) }
    }

    // Compiler Error
    // Protocol 'GamePointsDelegate' can only be used as a generic constraint because it has Self or associated type requirements
    var pointsDelegate: GamePointsDelegate?
}