简单地说，static是用于结构和枚举的静态函数，而class是用于类和协议吗？

这是主要的区别。其他一些不同之处在于类函数是动态调度的，并且可以被子类重写。

协议使用class关键字，但它并不排除structs实现协议，它们只是使用static。为协议选择了Class，这样就不必有第三个关键字来表示static或Class。

来自Chris Lattner关于这个话题：

我们考虑过统一语法（例如，使用“type”作为关键字），但这实际上并不简单。关键字“class”和“static”对于熟悉性很好，并且具有相当的描述性（一旦您理解了+方法的工作原理），并且为潜在地将真正静态的方法添加到类中打开了大门。这个模型的主要怪异之处在于，协议必须选择一个关键字（我们选择了“class”），但总的来说，这是一个正确的折衷。

下面的片段显示了类函数的一些重写行为：

class MyClass {
    class func myFunc() {
        println("myClass")
    }
}

class MyOtherClass: MyClass {
    override class func myFunc() {
        println("myOtherClass")
    }
}

var x: MyClass = MyOtherClass()
x.dynamicType.myFunc() //myOtherClass
x = MyClass()
x.dynamicType.myFunc() //myClass

更清楚地说，我在这里举个例子，

class ClassA {
  class func func1() -> String {
    return "func1"
  }

  static func func2() -> String {
    return "func2"
  }

  /* same as above
  final class func func2() -> String {
    return "func2"
  }
  */
}

静态函数与最终类函数相同

因为它是final，所以我们不能在子类中重写它，如下所示：

class ClassB : ClassA {
  override class func func1() -> String {
    return "func1 in ClassB"
  }

  // ERROR: Class method overrides a 'final` class method
  override static func func2() -> String {
    return "func2 in ClassB"
  }
}

我在操场上做了一些实验，得到了一些结论。

您可以看到，在类的情况下，使用类函数或静态函数只是一个习惯问题。

游乐场示例及说明：

class Dog {
    final func identity() -> String {
        return "Once a woofer, forever a woofer!"
    }

    class func talk() -> String {
        return "Woof woof!"
    }

    static func eat() -> String {
        return "Miam miam"
    }

    func sleep() -> String {
        return "Zzz"
    }
}

class Bulldog: Dog {
    // Can not override a final function
//    override final func identity() -> String {
//        return "I'm once a dog but now I'm a cat"
//    }

    // Can not override a "class func", but redeclare is ok
    func talk() -> String {
        return "I'm a bulldog, and I don't woof."
    }

    // Same as "class func"
    func eat() -> String {
        return "I'm a bulldog, and I don't eat."
    }

    // Normal function can be overridden
    override func sleep() -> String {
        return "I'm a bulldog, and I don't sleep."
    }
}

let dog = Dog()
let bullDog = Bulldog()

// FINAL FUNC
//print(Dog.identity()) // compile error
print(dog.identity()) // print "Once a woofer, forever a woofer!"
//print(Bulldog.identity()) // compile error
print(bullDog.identity()) // print "Once a woofer, forever a woofer!"

// => "final func" is just a "normal" one but prevented to be overridden nor redeclared by subclasses.


// CLASS FUNC
print(Dog.talk()) // print "Woof woof!", called directly from class
//print(dog.talk()) // compile error cause "class func" is meant to be called directly from class, not an instance.
print(Bulldog.talk()) // print "Woof woof!" cause it's called from Bulldog class, not bullDog instance.
print(bullDog.talk()) // print "I'm a bulldog, and I don't woof." cause talk() is redeclared and it's called from bullDig instance

// => "class func" is like a "static" one, must be called directly from class or subclassed, can be redeclared but NOT meant to be overridden.

// STATIC FUNC
print(Dog.eat()) // print "Miam miam"
//print(dog.eat()) // compile error cause "static func" is type method
print(Bulldog.eat()) // print "Miam miam"
print(bullDog.eat()) // print "I'm a bulldog, and I don't eat."

// NORMAL FUNC
//print(Dog.sleep()) // compile error
print(dog.sleep()) // print "Zzz"
//print(Bulldog.sleep()) // compile error
print(bullDog.sleep()) // print "I'm a bulldog, and I don't sleep."