Matrix extension http://coliru.stacked-crooked.com/a/672f92ed24a92cc9

gistfile1.txt

// Example program
#include <iostream>
#include <string>
#include <vector>


template<typename T>
void print(std::vector<T>& v)
{
    for(auto it : v)
        std::cout << it << " ";
        
    std::cout << '\n';
}

template<typename T>
std::vector<T> matrix_extend(std::vector<T>& v1, std::vector<T>& v2)
{
    std::cout << __PRETTY_FUNCTION__ << "\n";
    
    std::vector<int> ret;
    
    std::cout << "v1 " << v1.size() << '\n';
    print(v1);
    
    std::cout << "v2 " << v2.size() << '\n';
    print(v2);
    
    for(size_t i = 0; i < 3; i++)
    {
        for(size_t j = 0; j < (v1.size() / 3); j++)
        {
            ret.push_back(v1[i * (v1.size() / 3) + j]);
            print(ret);
        }
            
        for(size_t k = 0; k < (v2.size() / 3); k++)
        {
            ret.push_back(v2[i * (v2.size() / 3) + k]);
            print(ret);
        }
    }
    
    return ret;
}

template<typename T, typename... Args>
std::vector<T> matrix_extend(std::vector<T>& v1, std::vector<T>& v2, Args... args)
{
    std::cout << __PRETTY_FUNCTION__ << "\n";
    
    std::vector<int> ret;
    
    std::cout << "v1\n";
    print(v1);
    
    std::cout << "v2\n";
    print(v2);
    
    for(size_t i = 0; i < 3; i++)
    {
        for(size_t j = 0; j < (v1.size() / 3); j++)
        {
            ret.push_back(v1[i * (v1.size() / 3) + j]);
            print(ret);
        }
            
        for(size_t k = 0; k < (v2.size() / 3); k++)
        {
            ret.push_back(v2[i * (v2.size() / 3) + k]);
            print(ret);
        }
    }
    
    return matrix_extend(ret, args...);
}

int main()
{
    std::vector<int> v1 = {
        1, 1, 1,
        1, 1, 1,
        1, 1, 1
    };
    
    std::vector<int> v2 = {
        2, 2, 2,
        2, 2, 2,
        2, 2, 2
    };
        
    std::vector<int> v3 = {
        3, 3, 3,
        3, 3, 3,
        3, 3, 3
    };
    
    std::vector<int> v4 = {
        4, 4, 4,
        4, 4, 4,
        4, 4, 4
    };
    
    //std::vector<int> v = matrix_extend(v1, v2, v3);
    std::vector<int> v = matrix_extend(v1, v2, v3, v4);
    std::cout << __PRETTY_FUNCTION__ << "\n";
    
    print(v);
    

}