回答第一部分：限制模板功能

JesperE第二部分的答案正确。

1. Is there equivalent of <? extends T>, <? super T> in C++?

2. Also, does <? extends T>, <? super T> work even if T is an interface in Java?

answer to the first part: Restrict Template Function

JesperE has the answer right for the 2nd part.