Chaining filter, map, and reduce

We can chain filter, map, and reduce. The following lines declare a new calculateGamesHighestScoresSum method for our previously coded GameRepository class that chains filter, map, and reduce calls:

public func calculateGamesHighestScoresSum(minPlayedCount: Int) -> Int {
    return getAll().filter({ $0.playedCount >= minPlayedCount }).map({ $0.highestScore }).reduce(0) {
        sum, highestScore in
        return sum + highestScore
    }
}

The calculateGamesHighestScoresSum method receives a minPlayedCount argument of the Int type and returns an Int value. The code calls the getAll and filter methods to generate a new Array<Game> with only the Game instances, whose playedCount value is greater than or equal to the value specified in the minPlayedCount argument. The code calls the map method to transform an Array<Game> into an Array<Int> with the values specified in the highestScore stored property. Then, the code calls the reduce method...