Hands-On Design Patterns with C++

Non-type template parameters

Usually, template parameters are types, but C++ also allows for several kinds of non-type parameters. First of all, template parameters can be values of integer or enumeration types:

template <typename T, size_t N> class Array {    public:    T& operator[](size_t i) {        if (i >= N) throw std::out_of_range("Bad index");         return data_[i];    private:    T data_[N];};Array<int, 5> a;        // OKcin >> a[0];Array<int, a[0]> b;     // Error

This is a template with two parameters—the first is a type, but the second is not. It is a value of type size_t that determines the size of the array; the advantage of such a template over a built-in C-style array is that it can do range checking. The C++ standard library has a std::array class template ...