若要声明类型变量属性，请使用静态声明修饰符标记声明。类可以用类声明修饰符标记类型计算属性，以允许子类重写超类的实现。类型属性在类型属性中讨论。 请注意 在类声明中，关键字static与同时使用类和final声明修饰符标记声明具有相同的效果。

来源:Swift编程语言-类型变量属性

根据苹果公司发布的Swift 2.2 Book:

通过在方法的func关键字之前写入static关键字来指示类型方法。类也可以使用class关键字来允许子类重写父类对该方法的实现。”

为了更清楚，我举个例子，

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func与最终类func相同

因为它是final的，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。

博士TL;

如您所见，在类的情况下，使用类func还是静态func只是一个习惯问题。

游乐场的例子，并附有解释:

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."

static和class关键字都允许我们将方法附加到类而不是类的实例。例如，您可以创建一个具有名称和年龄等属性的Student类，然后创建一个静态方法numberOfStudents，该方法由Student类本身而不是单个实例拥有。

静态和类的不同之处在于它们支持继承的方式。当你创建一个静态方法时，它被类拥有，不能被子类改变，而当你使用类时，它可能会在需要时被覆盖。

下面是一个示例代码:

class Vehicle {
    static func getCurrentSpeed() -> Int {
        return 0
    }
    
    class func getCurrentNumberOfPassengers() -> Int {
        return 0
    } 
}

class Bicycle: Vehicle {
    //This is not allowed
    //Compiler error: "Cannot override static method"
    //static override func getCurrentSpeed() -> Int {
        //return 15
    //}
    
    class override func getCurrentNumberOfPassengers() -> Int {
        return 1
    }
}

若要声明类型变量属性，请使用静态声明修饰符标记声明。类可以用类声明修饰符标记类型计算属性，以允许子类重写超类的实现。类型属性在类型属性中讨论。 请注意 在类声明中，关键字static与同时使用类和final声明修饰符标记声明具有相同的效果。

来源:Swift编程语言-类型变量属性