SwiftにおけるBuilderパターンの実装 ref: http://qiita.com/rizumita/items/fe90d09a07d9b2d0e490

file0.txt

class A {
    var firstName: String?
    var lastName: String?
}

class B: A {
    var middleName: String?
}

file1.txt

protocol Buildable {
    typealias BuildType

    func build() -> BuildType
}

file2.txt

class ABuilder: Buildable {
    typealias BuildType = A

    private var firstName: String?
    private var lastName: String?

    func withFirstName(name: String) -> Self {
        firstName = name
        return self
    }

    func withLastName(name: String) -> Self {
        lastName = name
        return self
    }

    func build() -> A {
        let result = A()
        result.firstName = firstName
        result.lastName = lastName
        return result
    }
}

class BBuilder: ABuilder {
    typealias BuildType = B

    private var middleName: String?

    func withMiddleName(name: String) -> Self {
        self.middleName = name
        return self
    }

    override func build() -> B {
        let result = B()
        result.firstName = firstName
        result.middleName = middleName
        result.lastName = lastName
        return result
    }
}

file3.txt

let a = ABuilder()
    .withFirstName("First")
    .withLastName("Last")
    .build()
let b = BBuilder()
    .withFirstName("First")
    .withMiddleName("Middle")
    .withLastName("Last")
    .build()