Make second template functional of a unary_function

I'm a CS student, and the I have a task where I need some help. The task is to create a vectors_predicate_view class that gets a T type as first - and a predictatum template as a second parameter. In its constructor the class should get 2 std::vectors as parameters.

Here is the class:

#pragma once  #include <vector>    template<typename T, typename Predicate>  class vectors_predicate_view   {  private:      Predicate predict;      std::vector<T> originalContents1;      std::vector<T> originalContents2;        std::vector<T> &original1; // reference to original vector1      std::vector<T> &original2; // reference to original vector2        void setElements(std::vector<T> &vector1, std::vector<T> &vector2)      {          //Putting every element from vector1 into originalContents1          for(auto element : vector1)              originalContents1.push_back(element);          vector1.clear();    //Emptying vector1            //Putting every element from vector2 into originalContents2          for(auto element : vector2)              originalContents2.push_back(element);          vector2.clear();    //Emptying vector2            //We loop through originalContents1          //if the element gives back true for the predictatum, we add it to vector1          //else it goes to vector2          for(auto element : originalContents1)           {              if (predict(element))                  vector1.push_back(element);              else                  vector2.push_back(element);          }            //We loop through originalContents2          //if the element gives back true for the predictatum, we add it to vector1          for(auto element : originalContents2)              if(predict(element))                  vector1.push_back(element);      }    public:      vectors_predicate_view(std::vector<T> &vector1, std::vector<T> &vector2) : original1(vector1), original2(vector2)      {          setElements(vector1, vector2);      }  };  

The task is to make the second parameter optional, and if it's not given, the class should not do anything with the 2 given vectors inside its constructor.

Just to give an idea, here is how that second template optimally looks like. It's an std::unary_function that looks like this:

struct is_even: std::unary_function<int, bool>  {      bool operator()(int i) const      {          return 0 == i % 2;      }  };    struct is_good_language: std::unary_function<std::string, bool>  {      bool operator()(const std::string& s) const      {          return s == "C++" || s == "C";      }  };  

and called like this:

const vectors_predicate_view<int, is_even> va(a, b);  vectors_predicate_view<std::string, is_good_language> vb(x, y);  

Any help would be greatly appreciated!

from Recent Questions - Stack Overflow https://stackoverflow.com/questions/65376868/make-second-template-functional-of-a-unary-function Martin Serdült http://ifttt.com/images/no_image_card.png