它是这样工作的。试想一下,编译器改写了你的类变成这样:
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();
编译器的原因如下:如果接收器的类型是动物然后吃一定要到电话animal.VTable.AnimalEat。如果接收器的类型是Dog,则该呼叫必须是DogEat。因此,编译器写这些为:
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
也就是说正是它是如何工作的。编译器在后台为您生成vtables,并且根据重载分辨率的规则在编译时决定是否通过vtable调用。
当创建对象时,vtables由内存分配器设置。 (我的素描是这方面的一个谎言,因为虚函数表设置前的构造函数被调用,而不是之后。)
的“本”的虚方法实际上是秘密为一种无形的形式参数来传递方法。
有意义吗?
你知道Eric Lippert正在撰写关于这个主题的博客系列吗?请参阅http://blogs.msdn.com/b/ericlippert/archive/2011/03/17/implementing-the-virtual-method-pattern-in-c-part-one.aspx – Learner 2011-03-23 08:56:15
谢谢学习者。我正在关注它:) – Nishant 2011-04-05 03:03:14