How is a template instantiated?

Question

It\'s an exercise from C++ Primer 5th Edition:

Exercise 16.27: For each labeled statement explain what, if any, instantiations happen. If a tem

Answer 1

Regarding e and d I will quote the standard 14.7.1

Unless a function template specialization has been explicitly instantiated or explicitly specialized, the function template specialization is implicitly instantiated when the specialization is referenced in a context that requires a function definition to exist. Unless a call is to a function template explicit specialization or to a member function of an explicitly specialized class template, a default argument for a function template or a member function of a class template is implicitly instantiated when the function is called in a context that requires the value of the default argument.

Example also from the standard

template struct Z {
    void f();
    void g();
};

void h() {
    Z a;     // instantiation of class Z required
    Z* p;   // instantiation of class Z not required
    Z* q; // instantiation of class Z not required
    a.f();        // instantiation of Z::f() required
    p->g();       // instantiation of class Z required, and instantiation of Z::g() required
}

This means that no instantiation happens in d. While it will be instantiated in e if that function actually needed to call a function from that type ( could be a copy constructor or any other function called inside the function).