Swiftで「self」を返すメソッドを使ったメソッドチェーンの実装方法

class Example {
    var value: Int = 0

    func increment(by amount: Int) -> Example {
        self.value += amount
        return self
    }

    func multiply(by factor: Int) -> Example {
        self.value *= factor
        return self
    }
}

let result = Example()
    .increment(by: 5)
    .multiply(by: 3)

class Person {
    var name: String = ""
    var age: Int = 0
    var address: String = ""

    func setName(_ name: String) -> Person {
        self.name = name
        return self
    }

    func setAge(_ age: Int) -> Person {
        self.age = age
        return self
    }

    func setAddress(_ address: String) -> Person {
        self.address = address
        return self
    }

    func describe() -> String {
        return "Name: \(name), Age: \(age), Address: \(address)"
    }
}

let person = Person()
    .setName("John Doe")
    .setAge(30)
    .setAddress("123 Main St")

print(person.describe())
// 出力: Name: John Doe, Age: 30, Address: 123 Main St

let person = Person()
    .setName("John Doe")
    .setAge(30)
    .setAddress("123 Main St")

class Car {
    var make: String = ""
    var model: String = ""
    var year: Int = 0

    func setMake(_ make: String) -> Car {
        self.make = make
        return self
    }

    func setModel(_ model: String) -> Car {
        self.model = model
        return self
    }

    func setYear(_ year: Int) -> Car {
        self.year = year
        return self
    }

    func describe() -> String {
        return "Car: \(year) \(make) \(model)"
    }
}

let car = Car()
    .setMake("Toyota")
    .setModel("Corolla")
    .setYear(2021)

print(car.describe())
// 出力: Car: 2021 Toyota Corolla

class House {
    var rooms: Int = 0
    var hasGarage: Bool = false
    var hasGarden: Bool = false

    func setRooms(_ rooms: Int) -> House {
        self.rooms = rooms
        return self
    }

    func addGarage() -> House {
        self.hasGarage = true
        return self
    }

    func addGarden() -> House {
        self.hasGarden = true
        return self
    }

    func build() -> String {
        return "House with \(rooms) rooms, " +
               (hasGarage ? "a garage, " : "") +
               (hasGarden ? "a garden" : "no garden")
    }
}

let house = House()
    .setRooms(4)
    .addGarage()
    .addGarden()

print(house.build())
// 出力: House with 4 rooms, a garage, a garden

class APIRequest {
    var url: String = ""
    var method: String = "GET"
    var headers: [String: String] = [:]
    var body: String = ""

    func setURL(_ url: String) -> APIRequest {
        self.url = url
        return self
    }

    func setMethod(_ method: String) -> APIRequest {
        self.method = method
        return self
    }

    func setHeader(_ key: String, value: String) -> APIRequest {
        self.headers[key] = value
        return self
    }

    func setBody(_ body: String) -> APIRequest {
        self.body = body
        return self
    }

    func send() -> String {
        return "Sending \(method) request to \(url) with headers: \(headers) and body: \(body)"
    }
}

let request = APIRequest()
    .setURL("https://api.example.com/data")
    .setMethod("POST")
    .setHeader("Authorization", value: "Bearer token")
    .setBody("{'key':'value'}")

print(request.send())
// 出力: Sending POST request to https://api.example.com/data with headers: ["Authorization": "Bearer token"] and body: {'key':'value'}

class CustomView {
    var backgroundColor: String = "white"
    var cornerRadius: Int = 0
    var borderColor: String = "black"

    func setBackgroundColor(_ color: String) -> CustomView {
        self.backgroundColor = color
        return self
    }

    func setCornerRadius(_ radius: Int) -> CustomView {
        self.cornerRadius = radius
        return self
    }

    func setBorderColor(_ color: String) -> CustomView {
        self.borderColor = color
        return self
    }

    func describe() -> String {
        return "CustomView with background color: \(backgroundColor), corner radius: \(cornerRadius), border color: \(borderColor)"
    }
}

let view = CustomView()
    .setBackgroundColor("blue")
    .setCornerRadius(10)
    .setBorderColor("red")

print(view.describe())
// 出力: CustomView with background color: blue, corner radius: 10, border color: red

class Validator {
    var value: String?

    func setValue(_ value: String?) -> Validator {
        self.value = value
        return self
    }

    func validateNotEmpty() -> Validator? {
        guard let value = value, !value.isEmpty else {
            print("Error: Value is empty")
            return nil
        }
        return self
    }

    func validateMinLength(_ length: Int) -> Validator? {
        guard let value = value, value.count >= length else {
            print("Error: Value is too short")
            return nil
        }
        return self
    }
}

let validator = Validator()
    .setValue("Swift")
    .validateNotEmpty()?
    .validateMinLength(3)

if validator != nil {
    print("Validation passed")
} else {
    print("Validation failed")
}
// 出力: Validation passed

enum ValidationError: Error {
    case emptyValue
    case tooShort
}

class ResultValidator {
    var value: String?

    func setValue(_ value: String?) -> ResultValidator {
        self.value = value
        return self
    }

    func validateNotEmpty() -> Result<ResultValidator, ValidationError> {
        guard let value = value, !value.isEmpty else {
            return .failure(.emptyValue)
        }
        return .success(self)
    }

    func validateMinLength(_ length: Int) -> Result<ResultValidator, ValidationError> {
        guard let value = value, value.count >= length else {
            return .failure(.tooShort)
        }
        return .success(self)
    }
}

let result = ResultValidator()
    .setValue("S")
    .validateNotEmpty()
    .flatMap { $0.validateMinLength(3) }

switch result {
case .success:
    print("Validation passed")
case .failure(let error):
    switch error {
    case .emptyValue:
        print("Error: Value is empty")
    case .tooShort:
        print("Error: Value is too short")
    }
}
// 出力: Error: Value is too short

let validator = Validator()
    .setValue(nil)
    .validateNotEmpty() ?? Validator().setValue("Default").validateNotEmpty()

// 悪い例（長すぎるチェーン）
let person = Person()
    .setName("John")
    .setAge(30)
    .setAddress("123 Main St")
    .setPhone("555-5555")
    .setEmail("john@example.com")
    .setOccupation("Engineer")
    .setCompany("Tech Corp")

// 良い例（短いチェーンで区切る）
let person = Person()
    .setName("John")
    .setAge(30)

person
    .setAddress("123 Main St")
    .setPhone("555-5555")

// 悪い例（順序に依存）
let person = Person()
    .setAge(30)
    .setName("John")  // 名前を設定する前に年齢を設定する必要がある

// 良い例（順序に依存しない）
let person = Person()
    .setName("John")
    .setAge(30)

class Person {
    var name: String = ""
    var age: Int = 0

    func setName(_ name: String) -> Person {
        self.name = name
        return self
    }

    func setAge(_ age: Int) -> Person {
        self.age = age
        return self
    }
}

func testPersonNameSetting() {
    let person = Person().setName("John")
    XCTAssertEqual(person.name, "John")
}

func testPersonAgeSetting() {
    let person = Person().setAge(30)
    XCTAssertEqual(person.age, 30)
}

let book = Book()
    .setTitle("Swift Programming")
    .setAuthor("John Appleseed")
    .setPrice(29.99)

print(book.describe())
// 出力: Title: Swift Programming, Author: John Appleseed, Price: 29.99

let book = Book()
    .setTitle("")
    .setAuthor("John Appleseed")
    .setPrice(-10)

// 出力: Error: Title is empty
//        Error: Price must be greater than 0

let builder = BookBuilder()
builder.addBook()
    .setTitle("Swift Programming")
    .setAuthor("John Appleseed")
    .setPrice(29.99)
    .addBook()
    .setTitle("Advanced Swift")
    .setAuthor("Jane Doe")
    .setPrice(39.99)

builder.describeBooks()
// 出力: Book 1: Title: Swift Programming, Author: John Appleseed, Price: 29.99
//        Book 2: Title: Advanced Swift, Author: Jane Doe, Price: 39.99