我在利用继承方面的一般限制时,遇到了相当令人惊讶的情况。 我有超载方法<代码>Foo,与参数不同——无论是基础还是衍生的类别。 在这两种情况下,通常都会将案件转至超载方法的第二层楼――Bar。

When I call Foo with base class instance, Bar overload for the base class is called. When I call Foo with derived class instance, Bar overload for the derived class is called. This is clear and expected.

但当我试图合并<代码>时。 Foo methods into one GenericFoo that use generals and restrictions, methods are reflectedly - T is disabilities resolution, but only base-class overload of Bar.

public class Animal { }
public class Cat : Animal { }

public class AnimalProcessor
{
    public static void Foo(Animal obj)
    {
        Console.WriteLine("Foo(Animal)");
        Bar(obj);
    }

    public static void Foo(Cat obj)
    {
        Console.WriteLine("Foo(Cat)");
        Bar(obj);
    }

    // new generic method to replace the two above
    public static void GenericFoo<T>(T obj)
        where T : Animal
    {
        Console.WriteLine("Foo(generic)");
        Bar(obj);
    }

    public static void Bar(Animal obj)
    {
        Console.WriteLine("Bar(Animal)");
    }

    public static void Bar(Cat obj)
    {
        Console.WriteLine("Bar(Cat)");
    }
}

测试代码——非遗传性旧方法的头两例,新通用方法的两例。

Console.WriteLine("Animal()");
AnimalProcessor.Foo(new Animal());
Console.WriteLine();

Console.WriteLine("Cat()"); 
AnimalProcessor.Foo(new Cat());
Console.WriteLine();

Console.WriteLine("Animal()");
AnimalProcessor.GenericFoo(new Animal());
Console.WriteLine();

Console.WriteLine("Cat()"); 
AnimalProcessor.GenericFoo(new Cat());
Console.ReadLine();

And the result - note the difference in type resolved in Bar:

Animal()
Foo(Animal)
Bar(Animal)

Cat()
Foo(Cat)
Bar(Cat)

Animal()
Foo(generic)
Bar(Animal)

Cat()
Foo(generic)
Bar(Animal)

It looks like the compiler binds all calls from GenericFoo to the least specific overload, even if all more specific-typed calls are known at compile time. Why is that, what is the reason for such behaviour? Which part of specs defines this?