abstract_factory.swift

protocol AbstractGUIFactory {
    func createButton() -> Button
    func createWindow() -> Window
}

abstract_product.swift

protocol Button {
    func setTitle(_ title: String) -> Void
    func show() -> Void
}

protocol Window {
    func setTitle(_ title: String) -> Void
    func show() -> Void
}

concrete_factory.swift

class WinFactory : AbstractGUIFactory {
    func createButton() -> Button {
        return WinButton()
    }
    
    func createWindow() -> Window {
        return WinWindow()
    }
}

class OSXFactory : AbstractGUIFactory {
    func createButton() -> Button {
        return OSXButton()
    }
    
    func createWindow() -> Window {
        return OSXWindow()
    }
}

concrete_product.swift

class WinButton: Button {
    var title: String?
    
    func setTitle(_ title: String) -> Void {
        self.title = title
    }
    
    func show() -> Void {
        print("Showing Windows style button [Title: \(self.title!)]")
    }
}

class WinWindow : Window {
    var title: String?
    
    func setTitle(_ title: String) -> Void {
        self.title = title
    }
    
    func show() -> Void {
        print("Showing Windows style window [Title: \(self.title!)]")
    }
}

class OSXButton : Button {
    var title: String?
    
    func setTitle(_ title: String) -> Void {
        self.title = title
    }
    
    func show() -> Void {
        print("Showing OSX style button [Title: \(self.title!)]")
    }
}

class OSXWindow : Window {
    var title: String?
    
    func setTitle(_ title: String) -> Void {
        self.title = title
    }

    func show() -> Void {
        print("Showing OSX style window [Title: \(self.title!)]")
    }
}

GUIBuilder.swift

class GUIBuilder {
    private var platform: String
    private var guiFactory: AbstractGUIFactory?
    
    init(platform: String) {
        self.platform = platform
    }
    
    func initGuiFactory() -> Void {
        if nil != guiFactory { return }
        if platform == "Windows" { guiFactory = WinFactory() }
        else { guiFactory = OSXFactory() }
    }
    
    func buildButton() -> Button {
        initGuiFactory()
        return guiFactory!.createButton()
    }
    
    func buildWindow() -> Window {
        initGuiFactory()
        return guiFactory!.createWindow()
    }
}

main.swift

import Foundation

let guiBuilder: GUIBuilder = GUIBuilder(platform: "Windows")

let window: Window = guiBuilder.buildWindow()
window.setTitle("Mahbub")
window.show()

let button: Button = guiBuilder.buildButton()
button.setTitle("Connect")
button.show()