如何将A <T>类型的通用对象转换为A <T'>？

Question

I have a object of type MyClass<object> and I need to convert it to MyClass<int> as I know it is containing ints.

If I simply try to do the cast is does not compile:

MyClass<object> a = new MyClass<object>();
MyClass<int> b = (MyClass<int>) a;

What's wrong and how to do it?

Answer 1

You can go with implicit cast operator

class MyClass<T>
    {
        public static implicit operator MyClass<T>(MyClass<object> input)
        {
            return null;
        }
    }

and then the cast is valid

MyClass<object> a = new MyClass<object>();
MyClass<int> b = (MyClass<int>) a;

//you don't have to write cast type
MyClass<int> c = a;

though you still need to implement exact details of conversion.

EDIT : In case you want to call cast explicitely just change implicit keyword to explicit

class MyClass<T>
    {
        public static explicit operator MyClass<T>(MyClass<object> input)
        {
            return null;
        }
    }

which means that you can still use original cast but this becomes invalid

   //will not compile now !
   MyClass<object> a = new MyClass<object>();
   MyClass<int> b = a;

Answer 2

你不能，因为它们都不是另一个的超类。