你能在C＃中实例化一个泛型类型参数的嵌套类型吗？

Question

The following code results in a compiler error that I don't see should be necessary. Is there a good workaround?

error CS0704: A nested type cannot be specified through a type parameter `T'

public class Base<T>
{
    public T genericData;
    public Nested data;
    public class Nested
    {
    }

    public static B Create<B>() where B : Base<T>, new() {
        var result = new B();
        result.data = default(B.Nested);
        return result;
    }
}

Answer 1

Well, the complete name of Nested is actually Base<T>.Nested , nothing else. The Nested -class thus belongs to the Base<T> -class but not to its child-classes. Thus write the following instead:

result.data = default(Base<T>.Nested);

However the Base<T> -qualifier is redundant, as the code already is within that class. So you could also just use this:

result.data = default(Nested);

Apart from this you could also just use result.Data = null , as Base<T> is a reference-type, which defaults to null .