C++ Class 带 2 个模板 arguments、function 带 1 个参数

Question

Is there any way to call a class member function that takes only 1 template argument instead of 2?

I would like to write some code like this:

template<typename T, size_t N>
void Container<int, N>::quick_sort() {

}

Answer 1

You cannot partial specialize a method, you could partial specialize the whole class, but require some duplication.

template<typename T, size_t N>
class Container
{
    // Some code ...
    void quick_sort();
};

template <typename T,size_t N>
void Container<T, N>::quick_sort()
{
   // ...
}

// Class specialization
template <size_t N>
class Container<int, N>
{
    // Some similar/same code...
    void quick_sort();
};

template <size_t N>
void Container<int, N>::quick_sort()
{
   // ...
}

As alternative, C++17 allows

template<typename T, size_t N>
class Container
{
    // Some code ...
    void quick_sort()
    {
        if constexpr (std::is_same_v<int, T>) {
            // ...
        } else {
            // ...
        }
    }

};

For prior versions, regular if would probably produces error (both branches should be valid, even if not taken).

So tag dispatching is an easy approach (SFINAE is another one):

template <typename> struct Tag{};

template<typename T, size_t N>
class Container
{
private:

    void quick_sort(tag<int>)
    {
        // ...
    }
    template <typename U>
    void quick_sort(tag<U>)
    {
        // ...
    }

public:
    void quick_sort()
    {
        quick_sort(Tag<T>());
    }
    // Some code ...
};