它的工作原理是这样的。想象一下编译器将你的类重写为:
class VTable
{
public VTable(Func<Animal, string> eat)
{
this.AnimalEat = eat;
}
public readonly Func<Animal, string> AnimalEat;
}
class Animal
{
private static AnimalVTable = new VTable(Animal.AnimalEat);
private static string AnimalEat(Animal _this)
{
return "undefined";
}
public VTable VTable;
public static Animal CreateAnimal()
{
return new Animal()
{ VTable = AnimalVTable };
}
}
class Human : Animal
{
private static HumanVTable = new VTable(Human.HumanEat);
private static string HumanEat(Animal _this)
{
return "human";
}
public static Human CreateHuman()
{
return new Human()
{ VTable = HumanVTable };
}
}
class Dog : Animal
{
public static string DogEat(Dog _this) { return "dog"; }
public static Dog CreateDog()
{
return new Dog()
{ VTable = AnimalVTable } ;
}
}
现在考虑这些调用:
Animal animal;
Dog dog;
animal = new Human();
animal.Eat();
animal = new Animal();
animal.Eat();
dog = new Dog();
dog.Eat();
animal = dog;
animal.Eat();
编译器的理由如下:如果接收者的类型是 Animal,那么对 Eat 的调用必须是animal.VTable.AnimalEat。如果接收者的类型是 Dog,那么调用必须是 DogEat。所以编译器将它们写为:
Animal animal;
Dog dog;
animal = Human.CreateHuman(); // sets the VTable field to HumanVTable
animal.VTable.AnimalEat(animal); // calls HumanVTable.AnimalEat
animal = Animal.CreateAnimal(); // sets the VTable field to AnimalVTable
animal.VTable.AnimalEat(animal); // calls AnimalVTable.AnimalEat
dog = Dog.CreateDog(); // sets the VTable field to AnimalVTable
Dog.DogEat(dog); // calls DogEat, obviously
animal = dog;
animal.VTable.AnimalEat(animal); // calls AnimalVTable.AnimalEat
That is exactly怎么运行的。编译器在幕后为您生成 vtable,并且在编译时根据重载决策规则决定是否通过vtable调用.
vtables是在创建对象时由内存分配器设置的。 (我的草图在这方面是一个谎言,因为 vtable 已设置before演员被召唤,而不是之后。)
虚方法的“this”实际上是作为一个不可见的形参秘密地传递给该方法的。
合理?