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c++templatesexplicit-instantiation

When would you use template explicit instantiation?

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?

Solution

  • 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
}