How to pass vector

The question is related to a talk by Stefanus Du Toit on hourglass pattern. Its a great talk, really helpful for library writers.

Youtube Link: https://youtu.be/PVYdHDm0q6Y

Slideshare Link: http://ift.tt/1AGuMgW

Ok here is the question:

Say I have to pass a std::vector<MyObject> across the library boundary. What is the best way to do this using hourglass pattern. I am concerned about the performance as well as keeping a clean interface. Given below is a set of example interfaces that I want to implement.

Clientside C++ interface:

void MyLibraryClass::DoSomething(const std::vector<MyObject>& objs);

C Interface:

???? (Not sure what is the best practice here)

Internall library C++ interface:

MyInternalLibraryClass::DoSomething(const std::vector<MyObjectImpl>& objs);

Hope this explains my question.