Swift Language
Programmation fonctionnelle dans Swift

Extraire une liste de noms d'une liste de personne (s)

Étant donné une Person struct

struct Person {
    let name: String
    let birthYear: Int?
}

et un tableau de Person(s)

let persons = [
    Person(name: "Walter White", birthYear: 1959),
    Person(name: "Jesse Pinkman", birthYear: 1984),
    Person(name: "Skyler White", birthYear: 1970),
    Person(name: "Saul Goodman", birthYear: nil)
]

nous pouvons récupérer un tableau de String contenant la propriété name de chaque personne.

let names = persons.map { $0.name }
// ["Walter White", "Jesse Pinkman", "Skyler White", "Saul Goodman"]

Traversée

let numbers = [3, 1, 4, 1, 5]
// non-functional
for (index, element) in numbers.enumerate() {
    print(index, element)
}

// functional
numbers.enumerate().map { (index, element) in
    print((index, element))
}

En saillie

Appliquer une fonction à une collection / flux et créer une nouvelle collection / flux s'appelle une projection .

/// Projection
var newReleases = [
    [
        "id": 70111470,
        "title": "Die Hard",
        "boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
        "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
        "rating": [4.0],
        "bookmark": []
    ],
    [
        "id": 654356453,
        "title": "Bad Boys",
        "boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
        "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
        "rating": [5.0],
        "bookmark": [[ "id": 432534, "time": 65876586 ]]
    ],
    [
        "id": 65432445,
        "title": "The Chamber",
        "boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
        "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
        "rating": [4.0],
        "bookmark": []
    ],
    [
        "id": 675465,
        "title": "Fracture",
        "boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
        "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
        "rating": [5.0],
        "bookmark": [[ "id": 432534, "time": 65876586 ]]
    ]
]


var videoAndTitlePairs = [[String: AnyObject]]()
newReleases.map { e in
    videoAndTitlePairs.append(["id": e["id"] as! Int, "title": e["title"] as! String])
}

print(videoAndTitlePairs)

Filtration

La création d'un flux en sélectionnant les éléments d'un flux qui passe une certaine condition est appelée filtrage

var newReleases = [
    [
        "id": 70111470,
        "title": "Die Hard",
        "boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
        "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
        "rating": 4.0,
        "bookmark": []
    ],
    [
        "id": 654356453,
        "title": "Bad Boys",
        "boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
        "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
        "rating": 5.0,
        "bookmark": [[ "id": 432534, "time": 65876586 ]]
    ],
    [
        "id": 65432445,
        "title": "The Chamber",
        "boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
        "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
        "rating": 4.0,
        "bookmark": []
    ],
    [
        "id": 675465,
        "title": "Fracture",
        "boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
        "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
        "rating": 5.0,
        "bookmark": [[ "id": 432534, "time": 65876586 ]]
    ]
]

var videos1 = [[String: AnyObject]]()
/**
 *  Filtering using map
 */
newReleases.map { e in
    if e["rating"] as! Float == 5.0 {
        videos1.append(["id": e["id"] as! Int, "title": e["title"] as! String])
    }
}

print(videos1)

var videos2 = [[String: AnyObject]]()
/**
 *  Filtering using filter and chaining
 */
newReleases
    .filter{ e in
        e["rating"] as! Float == 5.0
    }
    .map { e in
    videos2.append(["id": e["id"] as! Int, "title": e["title"] as! String])
}

print(videos2)

Utiliser un filtre avec Structs

Vous souhaiterez peut-être fréquemment filtrer les structures et autres types de données complexes. La recherche d'un tableau de structures pour des entrées contenant une valeur particulière est une tâche très courante et facilement réalisée dans Swift à l'aide de fonctions de programmation fonctionnelles. De plus, le code est extrêmement succinct.

struct Painter {
    enum Type { case Impressionist, Expressionist, Surrealist, Abstract, Pop }
    var firstName: String
    var lastName: String
    var type: Type
}

let painters = [
    Painter(firstName: "Claude", lastName: "Monet", type: .Impressionist),
    Painter(firstName: "Edgar", lastName: "Degas", type: .Impressionist),
    Painter(firstName: "Egon", lastName: "Schiele", type: .Expressionist),
    Painter(firstName: "George", lastName: "Grosz", type: .Expressionist),
    Painter(firstName: "Mark", lastName: "Rothko", type: .Abstract),
    Painter(firstName: "Jackson", lastName: "Pollock", type: .Abstract),
    Painter(firstName: "Pablo", lastName: "Picasso", type: .Surrealist),
    Painter(firstName: "Andy", lastName: "Warhol", type: .Pop)
]

// list the expressionists
dump(painters.filter({$0.type == .Expressionist}))

// count the expressionists
dump(painters.filter({$0.type == .Expressionist}).count)    
// prints "2"

// combine filter and map for more complex operations, for example listing all
// non-impressionist and non-expressionists by surname
dump(painters.filter({$0.type != .Impressionist && $0.type != .Expressionist})
    .map({$0.lastName}).joinWithSeparator(", "))  
// prints "Rothko, Pollock, Picasso, Warhol"