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  1. #include <utility>
  2.  
  3. template< typename BinaryFunc, typename First, typename... Types >
  4. struct helper;
  5.  
  6. template< typename BinaryFunc, typename First>
  7. struct helper<BinaryFunc, First> {
  8.     typedef decltype(std::declval<First>()) type;
  9. };
  10.  
  11. template< typename BinaryFunc, typename First, typename Second >
  12. struct helper<BinaryFunc, First, Second> {
  13.     typedef decltype(
  14.         std::declval<BinaryFunc>()( std::declval<First>(), std::declval<Second>() )
  15.     ) type;
  16. };
  17.  
  18. template< typename BinaryFunc, typename First, typename Second, typename... Rest >
  19. struct helper<BinaryFunc, First, Second, Rest...>  {
  20.     typedef typename helper< BinaryFunc,
  21.                              typename helper<BinaryFunc, First, Second>::type,
  22.                              Rest...
  23.                            >::type
  24.                      type;
  25. };
  26.  
  27. template< typename BinaryFunc, typename First, typename Second >
  28. typename helper<BinaryFunc, First, Second>::type
  29. foldl( BinaryFunc&& func, First&& first, Second&& second ) {
  30.     return func( std::forward<First>(first), std::forward<Second>(second) );
  31. }
  32.  
  33. template< typename BinaryFunc, typename First, typename Second, typename... Rest >
  34. typename helper<BinaryFunc, First, Second, Rest...>::type
  35. foldl( BinaryFunc&& func, First&& first, Second&& second, Rest&&... rest ) {
  36.    return foldl(
  37.       std::forward<BinaryFunc>(func),
  38.       func( std::forward<First>(first), std::forward<Second>(second) ),
  39.       std::forward<Rest>(rest)...
  40.    );
  41. }
  42.  
  43. struct adder
  44. {
  45.    template< int LHS, int RHS >
  46.    std::integral_constant<int,LHS+RHS>
  47.    operator()( std::integral_constant<int,LHS>, std::integral_constant<int,RHS> )
  48.    {
  49.       return {};
  50.    }
  51. };
  52.  
  53. int main() {
  54.     foldl( adder(),
  55.       std::integral_constant<int,1>{},
  56.       std::integral_constant<int,2>{},
  57.       std::integral_constant<int,3>{},
  58.       std::integral_constant<int,4>{}
  59.     );
  60.     return 0;
  61. }
Success #stdin #stdout 0s 3336KB
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https://ideone.com/JWkmBo
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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