我可以在Swift库中看到这些定义:
extension Bool : BooleanLiteralConvertible {
static func convertFromBooleanLiteral(value: Bool) -> Bool
}
protocol BooleanLiteralConvertible {
typealias BooleanLiteralType
class func convertFromBooleanLiteral(value: BooleanLiteralType) -> Self
}
定义为静态func的成员函数和定义为类func的成员函数之间有什么区别?是不是简单地说，static是用于结构体和枚举的静态函数，class是用于类和协议?还有其他不同之处吗?在语法本身中有这种区别的基本原理是什么?
当前回答
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."
其他回答
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"
}
}
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
这被称为类型方法，并且像实例方法一样使用点语法调用。但是，在类型上调用类型方法，而不是在该类型的实例上调用类型方法。下面是如何在一个名为SomeClass的类上调用类型方法:
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."
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。”
