A very lightweight ServiceLocator implementation including a module mechanism written in Swift.

ServiceLocator.swift

import Foundation

public protocol ServiceLocatorModul {
	func registerServices(serviceLocator: ServiceLocator)
}

public class ServiceLocator {
	private var registry = [ObjectIdentifier:Any]()

	public static var sharedLocator = ServiceLocator()

	init() {
		registerModules([CocoaDefaultModul()])
	}

	// MARK: Registration

	public func register<Service>(factory: () -> Service) {
		let serviceId = ObjectIdentifier(Service.self)
		registry[serviceId] = factory
	}

	public static func register<Service>(factory: () -> Service) {
		sharedLocator.register(factory)
	}

	public func registerSingleton<Service>(singletonInstance: Service) {
		let serviceId = ObjectIdentifier(Service.self)
		registry[serviceId] = singletonInstance
	}

	public static func registerSingleton<Service>(singletonInstance: Service) {
		sharedLocator.registerSingleton(singletonInstance)
	}

	public func registerModules(modules: [ServiceLocatorModul]) {
		modules.forEach { $0.registerServices(self) }
	}

	public static func registerModules(modules: [ServiceLocatorModul]) {
		sharedLocator.registerModules(modules)
	}

	// MARK: Injection

	public static func inject<Service>() -> Service {
		return sharedLocator.inject()
	}

	// This method is private because no service which wants to request other services should
	// bind itself to specific instance of a service locator.
	private func inject<Service>() -> Service {
		let serviceId = ObjectIdentifier(Service.self)
		if let factory = registry[serviceId] as? () -> Service {
			return factory()
		} else if let singletonInstance = registry[serviceId] as? Service {
			return singletonInstance
		} else {
			fatalError("No registered entry for \(Service.self)")
		}
	}

}

class CocoaDefaultModul: ServiceLocatorModul {
	func registerServices(serviceLocator: ServiceLocator) {
		serviceLocator.register { NSNotificationCenter.defaultCenter() }
		serviceLocator.register { NSUserDefaults.standardUserDefaults() }

		serviceLocator.register { NSURLSession.sharedSession() }

		serviceLocator.register { UIScreen.mainScreen() }
		serviceLocator.register { UIApplication.sharedApplication() }
		serviceLocator.register { UIApplication.sharedApplication().delegate! }
	}
}