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  1. #include <iostream>
  2. #include <functional>
  3. #include <initializer_list>
  4.  
  5. template<typename Functor, typename T, size_t N>
  6. T constexpr reduce(Functor f, T(&arr)[N]) {
  7. 	typename std::remove_const<T>::type val = arr[0];
  8. 	for(auto i = std::begin(arr)+1; i != std::end(arr); ++i) val = f(val, *i);
  9. 	return val;	
  10. }
  11.  
  12. template<typename Functor, typename T>
  13. T constexpr reduce(Functor f, std::initializer_list<T> il) {
  14. 	T val = *il.begin();
  15. 	for(auto i = il.begin()+1; i != il.end(); ++i) val = f(val, *i);
  16. 	return val;
  17. }
  18.  
  19. template<typename Functor, typename T, typename... Ts>
  20. T constexpr reduce(Functor f, T t1, Ts... ts) {
  21.   return f(t1, reduce(f, std::initializer_list<T>({ts...})));
  22. }
  23.  
  24. template<int value>
  25. void print_constexpr() { std::cout << value << std::endl; }
  26.  
  27. int main() {
  28. 	// run-time or compile-time
  29. 	std::cout << reduce(std::plus<int>(), 1, 2, 3, 4, 5, 6, 7) << std::endl;  // 28
  30. 	std::cout << reduce(std::plus<int>(), {1, 2, 3, 4, 5, 6, 7}) << std::endl;// 28
  31. 	const int input[3] = {1, 2, 3};   // 6
  32. 	std::cout << reduce(std::plus<int>(), input) << std::endl;
  33.  
  34. 	// compile-time
  35. 	print_constexpr< reduce(std::plus<int>(), 1, 2, 3, 4, 5, 6, 7) >(); 	// 28 
  36. 	print_constexpr< reduce(std::plus<int>(), {1, 2, 3, 4, 5, 6, 7}) >(); 	// 28 
  37. 	constexpr int input_constexpr[3] = {1, 2, 3};   // 6
  38. 	print_constexpr< reduce(std::plus<int>(), input_constexpr) >(); // 6 
  39.  
  40. 	return 0;
  41. }
Success #stdin #stdout 0s 3412KB
comments (?)
stdin 
Standard input is empty
stdout 
28
28
6
28
28
6
https://ideone.com/nM8HH3
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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