Class template with array or vector arguments

Question

I need to write a class template definition with two template parameters (type , functor) and two template arguments (array/std::vector , int) that can execute the following code:

    const char* message= "Message";

    const transform<char, firstFunctor> first(message, lengthOfMessage);

    transform_view<int, secondFunctor> second(intArray, intSize);

    transform<double, thirdFunctor> third(doubleArray, doubleSize);

The type of the array/ vector has to match the type of the first template parameter.

I tried some variations like this:

   template <typename A, typename B>
   class transform
   {
   public:
    transform<A, B>(A[], B) {...};
   }

But I could not get the constructor's first parameter to match all of the three types.

Any advice is appreciated, thanks!

Answer 1

you wrote the definition of the constructor incorrectly.

transform<A, B>(A[], B) {...}; you will pass a vector, so why did you write A[] as a parameter type?

You need something like the following

#include <iostream>

template <typename T>
struct functor{
    void operator()(const T array [], size_t sze) {
        for (int i{}; i < sze; ++i) {
            std::cout << array[i] << " ";
        }
        std::cout << "\n";
    }
};

template<typename T, typename Function>
class transform {
    const T* array;
    size_t sze;
    Function functor{};
public:
    transform(const T array [], size_t sze):array{array}, sze{sze}{
        functor(array, sze);

    }
};

template< typename T, typename E>
using transform_view =  transform<T, E>;


int main()
{
    using firstFunctor = functor<char>;
    using secondFunctor = functor<int>;
    using thirdFunctor = functor<double>;
    const char *message = "Message";
    size_t lengthOfMessage = 7;

    int intArray[] = {1, 3};
    size_t intSize = 2;

    double doubleArray[] = {1.4, 3.2};
    size_t doubleSize = 2;

    //The given three lines
    const transform<char, firstFunctor> first(message, lengthOfMessage);

    transform_view<int, secondFunctor> second(intArray, intSize);

    transform<double, thirdFunctor> third(doubleArray, doubleSize);
}
The output
M e s s a g e
1 3
1.4 3.2