Hands-On Design Patterns with Swift

A recommendation engine

A recommendation engine can be thought of as a software system that gives you the most relevant answer based on a list of objects:

protocol RecommendationEngine {    associatedtype Model    var models: [Model] { get }    func filter(elements: [Model]) -> [Model]    func sort(elements: [Model]) -> [Model]}

We build our recommendation engine around two core methods—one for filtering out the undesired objects and the other around sorting; the most relevant results are always first.

Thanks to protocol extensions, we're able to provide the default implementation for the matching algorithm:

extension RecommendationEngine {    func match() -> Model? {        // If we only have 0 or 1 models, no need to run the algorithm        guard models.count >