to have done 与having done 有什么区别

to have done 一般指尚未完成的完成时,属于完成时语态,例如 By the end of next term(尚
未来到) ,we are going to have learnt nine thousand words.
而having done 强调时间上的先后顺序,一般作状语,例如 Having finished
his work,Bob went back home happily.