如何在 Swift 中获取类的实例化类型？

Question

我是一名 C# 程序员，试图了解 Swift 的类型系统。下面的代码定义了一个带有访问器getTypeOfFruit() 的超类fruit。我希望它返回实例化类型而不是超类的类型。

旁白：有没有关于 Swift 类型系统的高级文档？我遇到的大部分内容都只涉及基础知识。

public class Fruit {
    private var fruitType = Fruit.Type.self      // generic fruit type
    public func getTypeOfFruit<T>() -> T.Type  { 
        return fruitType as! T.Type              //
    }
}

public class Apple: Fruit { 

}

public class TimApple: Apple {
}

var fruit = Fruit.self        // error:  Instance member 'getTypeOfFruit' cannot be used
print(fruit.getTypeOfFruit()) // should print "Fruit"

var fruit = Apple.self
print(fruit.getTypeOfFruit()) // should print "Apple"

fruit = TimApple.self
print(fruit.getTypeOfFruit()) // should print "TimApple"

Answer 1

您可以使用type(of:)，例如，

public class Fruit {
    public func getTypeOfFruit() -> Fruit.Type  {
        return type(of: self)
    }
}

public class Apple: Fruit { }

public class TimApple: Apple { }

var fruit = Fruit()
print(fruit.getTypeOfFruit()) // prints "Fruit"

fruit = Apple()
print(fruit.getTypeOfFruit()) // prints "Apple"

fruit = TimApple()
print(fruit.getTypeOfFruit()) // print "TimApple"