// fig14_16.cpp
// Demonstrating function objects.
#include <array> 
#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <numeric> 

// binary function returns the sum of its first argument total 
// and the square of its second argument value
int sumSquares(int total, int value) {
   return total + value * value;
}

// class SumSquaresClass defines overloaded operator()
// that returns the sum of its first argument total 
// and the square of its second argument value               
class SumSquaresClass {
public:
   // add square of value to total and return result           
   int operator()(int total, int value) {
      return total + value * value;
   }
};

int main() {
   std::array integers{1, 2, 3, 4};
   std::ostream_iterator<int> output{std::cout, " "};

   std::cout << "array integers contains: ";
   std::ranges::copy(integers, output);

   // calculate sum of squares of elements of array integers
   // using binary function sumSquares                      
   int result{std::accumulate(integers.cbegin(), integers.cend(),
      0, sumSquares)};

   std::cout << "\n\nSum of squares\n"
      << "via binary function sumSquares: " << result;

   // calculate sum of squares of elements of array integers
   // using binary function object                           
   result = std::accumulate(integers.cbegin(), integers.cend(),
      0, SumSquaresClass{});

   std::cout << "\nvia a SumSquaresClass function object: " << result;

   // calculate sum of squares array
   result = std::accumulate(integers.cbegin(), integers.cend(),
      0, [](auto total, auto value) {return total + value * value; });

   std::cout << "\nvia a lambda: " << result << "\n";
}


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