Content of class method determined by the template value-CodePudding

By using c 14 or c 11, do we have an elegant approach to do the following task? Number of members and type of operations are determined by the template input value 'count'

    template<int count>
    class show{
    public:
        run(){
            if (count == 1){
                int x;
            } else if(count ==2){
                int x, y;
            }else if(count ==3){
                int x, y, z;
            } 

            if (count == 1){
                printf("res: %d \n", x);
            } else if(count ==2){
                printf("res: %d \n", x y);
            }else if(count ==3){
                printf("res: %d \n", x y z);
            } 

        }
    };

Update: can we use partial specialization or something related to the template in this case?

CodePudding user response：

In your case, an array (std::array) seems appropriate:

template <std::size_t count>
class show
{
public:
    std::array<int, count> data{};
    // ...
    void run()
    {
        const int sum = std::accumulate(data.begin(), data.end(), 0);
        printf("res: %d \n", sum);
    }
};

CodePudding user response：

Yes, you can use specialization:

template<int count>
class show;

template<>
class show<1>{
    int x;
    public:
    show(int _x):x{_x}{}
    void run(){
        std::cout << "val of x " << x << std::endl;
    }   
};



template<>
class show<2>{
    int x,y;
    public:
    show(int _x, int _y):x{_x}, y{_y}{}
    void run(){
        std::cout << "add " << x y << std::endl;
    }   
};

But you also can have it more generic:

template <int count>
class simply
{
    std::array<int, count> arr;

    public:
    template < typename ... T > 
        simply( T ... in ): arr{ in... } {}

    void run()
    {   
        std::cout << [this](){ int sum=0; for( auto el: arr ){ sum =el; } return sum; }() << std::endl;
    }   
};

To use all the stuff above:

int main() {
    show<1> s1(10);
    show<2> s2(100,200);

    s1.run();
    s2.run();

    simply<4> si( 1,2,3,4 );
    si.run();
}

Remarks: You should add some more stuff to simply to check that all parameters of type int with sfinae or static_assert. But his is another question ...