How to use explicit template instantiation to reduce compilation time?

Question

It was suggested to use explicit template instantiation to reduce compilation time. I am wondering how to do it. For example

// a.h
template         


        

Answer 1

Declare the instantiation in the header:

extern template class A;

and define it in one source file:

template class A;

Now it will only be instantiated once, not in every translation unit, which might speed things up.