final class MySingleton {
     private init() {}
     static let shared = MySingleton()
}

那就叫它;

let shared = MySingleton.shared

Swift单例在Cocoa框架中作为类函数公开，例如NSFileManager.defaultManager()， NSNotificationCenter.defaultCenter()。因此，作为一个类函数来反映这种行为比作为其他解决方案的类变量更有意义。例句:

class MyClass {

    private static let _sharedInstance = MyClass()

    class func sharedInstance() -> MyClass {
        return _sharedInstance
    }
}

通过MyClass.sharedInstance()检索单例。

这里有一个Jack Wu/hpique的嵌套结构实现的单例实现示例，仅供参考。实现还展示了如何进行归档，以及一些附带的功能。我找不到这么完整的例子，希望这能对大家有所帮助!

import Foundation

class ItemStore: NSObject {

    class var sharedStore : ItemStore {
        struct Singleton {
            // lazily initiated, thread-safe from "let"
            static let instance = ItemStore()
        }
        return Singleton.instance
    }

    var _privateItems = Item[]()
    // The allItems property can't be changed by other objects
    var allItems: Item[] {
        return _privateItems
    }

    init() {
        super.init()
        let path = itemArchivePath
        // Returns "nil" if there is no file at the path
        let unarchivedItems : AnyObject! = NSKeyedUnarchiver.unarchiveObjectWithFile(path)

        // If there were archived items saved, set _privateItems for the shared store equal to that
        if unarchivedItems {
            _privateItems = unarchivedItems as Array<Item>
        } 

        delayOnMainQueueFor(numberOfSeconds: 0.1, action: {
            assert(self === ItemStore.sharedStore, "Only one instance of ItemStore allowed!")
        })
    }

    func createItem() -> Item {
        let item = Item.randomItem()
        _privateItems.append(item)
        return item
    }

    func removeItem(item: Item) {
        for (index, element) in enumerate(_privateItems) {
            if element === item {
                _privateItems.removeAtIndex(index)
                // Delete an items image from the image store when the item is 
                // getting deleted
                ImageStore.sharedStore.deleteImageForKey(item.itemKey)
            }
        }
    }

    func moveItemAtIndex(fromIndex: Int, toIndex: Int) {
        _privateItems.moveObjectAtIndex(fromIndex, toIndex: toIndex)
    }

    var itemArchivePath: String {
        // Create a filepath for archiving
        let documentDirectories = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.UserDomainMask, true)
        // Get the one document directory from that list
        let documentDirectory = documentDirectories[0] as String
        // append with the items.archive file name, then return
        return documentDirectory.stringByAppendingPathComponent("items.archive")
    }

    func saveChanges() -> Bool {
        let path = itemArchivePath
        // Return "true" on success
        return NSKeyedArchiver.archiveRootObject(_privateItems, toFile: path)
    }
}

如果你不认识其中的一些函数，这里有一个我一直在使用的小Swift实用程序文件:

import Foundation
import UIKit

typealias completionBlock = () -> ()

extension Array {
    func contains(#object:AnyObject) -> Bool {
        return self.bridgeToObjectiveC().containsObject(object)
    }

    func indexOf(#object:AnyObject) -> Int {
        return self.bridgeToObjectiveC().indexOfObject(object)
    }

    mutating func moveObjectAtIndex(fromIndex: Int, toIndex: Int) {
        if ((fromIndex == toIndex) || (fromIndex > self.count) ||
            (toIndex > self.count)) {
                return
        }
        // Get object being moved so it can be re-inserted
        let object = self[fromIndex]

        // Remove object from array
        self.removeAtIndex(fromIndex)

        // Insert object in array at new location
        self.insert(object, atIndex: toIndex)
    }
}

func delayOnMainQueueFor(numberOfSeconds delay:Double, action closure:()->()) {
    dispatch_after(
        dispatch_time(
            DISPATCH_TIME_NOW,
            Int64(delay * Double(NSEC_PER_SEC))
        ),
        dispatch_get_main_queue()) {
            closure()
    }
}

这是具有线程安全功能的最简单的一个。即使其他线程想要访问同一个单例对象，它们也不能访问。斯威夫特3/4

struct DataService {

    private static var _instance : DataService?

    private init() {}   //cannot initialise from outer class

    public static var instance : DataService {
        get {
            if _instance == nil {
                DispatchQueue.global().sync(flags: .barrier) {
                    if _instance == nil {
                        _instance = DataService()
                    }
                }
            }
            return _instance!
        }
    }
}

我要求我的单例允许继承，而这些解决方案实际上都不允许。所以我想到了这个:

public class Singleton {
    private static var sharedInstanceVar = Singleton()

    public class func sharedInstance() -> Singleton {
        return sharedInstanceVar
    }
}


public class SubSingleton: Singleton {

    private static var sharedInstanceToken: dispatch_once_t = 0

    public class override func sharedInstance() -> SubSingleton {
        dispatch_once(&sharedInstanceToken) {
            sharedInstanceVar = SubSingleton()
        }
    return sharedInstanceVar as! SubSingleton
    }
}

这样，当首先执行Singleton. sharedinstance()时，它将返回Singleton的实例 当首先执行SubSingleton. sharedinstance()时，它将返回创建的SubSingleton实例。 如果执行了上述操作，则SubSingleton.sharedInstance() is Singleton为true，并且使用相同的实例。

第一种脏方法的问题是，我不能保证子类会实现dispatch_once_t，并确保每个类只修改一次sharedInstanceVar。

我将尝试进一步完善它，但是看看是否有人对此有强烈的反对(除了它很冗长并且需要手动更新之外)，这将是很有趣的。

有更好的办法。你可以像这样在你的类声明上面声明一个全局变量:

var tpScopeManagerSharedInstance = TPScopeManager()

这只是调用你的默认init或任何init和全局变量是dispatch_once在Swift默认。然后在任何你想要引用的类中，你只需要这样做:

var refrence = tpScopeManagerSharedInstance
// or you can just access properties and call methods directly
tpScopeManagerSharedInstance.someMethod()

所以基本上你可以去掉整个共享实例代码块。