Question

I’m a beginner in C++ and using the book “C++ Primer Plus” to teach myself the language as well as to become more comfortable in programming.

I was doing some excersises in the book which are related to the topic of function templates and I have two questions.

I don’t understand why the following explicit specialization doesn’t work:

template <typename T>
T lesser(T a, T b)
{
        return a > b ? a : b;
}


template <> 
box lesser<box>(box& a, box& b)
{
        return a.volume > b.volume? a : b;
}

Assuming I have a structure of type box, why is it not possible to specialize the type to type “box&” but to type “box”? The second declaration means “Don’t use lesser() template to generate a function definition. Instead, use a seperate, specialized function”. And still, I can’t use type box&, only type box. Why is that?

edit: Ok, the second problem just disappeard by itself.

Answer 1

You have to specialize T to the same type in every instance:

template <>
box& lesser<box&>(box& a, box& b)
{
    // ...
}

Or you could use box in every case.

---

Alternatively, you could change your template to something like:

template <typename T>
T lesser(const T& a, const T& b)
{
        return a > b ? a : b;
}

and specialize it as

template <>
box lesser(const box& a, const box& b)
{
        // ...
}