Creating a blank window on macOS

BlankApp.swift

import Cocoa

final class App {
	private static var shared: App?

	static func main() {
		shared = App()
	}

	// MARK: -
	let window = NSWindow()

	private init() {
		_ = NSApplication.shared
		NSApp.setActivationPolicy(.regular)
		NSApp.activate(ignoringOtherApps: true)
		
		let bar = NSMenu()
		let barItem = NSMenuItem()
		let menu = NSMenu()
		let quit = NSMenuItem(title: "Quit", action: #selector(terminate), keyEquivalent: "q")
		bar.addItem(barItem)
		barItem.submenu = menu
		menu.addItem(quit)
		NSApp.mainMenu = bar
		
		// Window.
		window.setFrame(NSRect(x: 0, y: 0, width: 500, height: 500), display: false)
		window.styleMask = NSWindow.StyleMask(rawValue: 0xf)
		window.backingType = .buffered
		window.center()
		window.title = "NSApplication test"
		window.makeKeyAndOrderFront(nil)

		window.contentView = NSView()
		
		NSApp.run()
	}
	
	@objc private func terminate() {
		exit(0)
	}
}

App.main()