Question

I’ve just been reading about template explicit instantiation:

template struct MyStruct<long>;

It was described as “quite rare”, so under what circumstances would it be useful?

Answer 1

One of the use cases is to hide definitions from the end-user.

tpl.h:

template<typename T>
void func(); // Declaration

tpl.cpp:

template<typename T>
void func()
{
    // Definition
}

template void func<int>(); // explicit instantiation for int
template void func<double>();  // explicit instantiation for double

main.cpp

#include "tpl.h"
int main()
{
    func<double>(); // OK
    func<int>(); // OK
    // func<char>(); - Linking ERROR
}