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  1. #include <iostream>
  2. #include <vector>
  3. #include <utility>
  4.  
  5.     template<typename T, typename U, typename A1, typename A2>
  6.     decltype(std::declval<T>() * std::declval<U>() + std::declval<T>() * std::declval<U>())
  7.     dot_product( std::vector<T, A1> const& lhs, std::vector<U, A2> const& rhs )
  8.     {
  9.       decltype(std::declval<T>() * std::declval<U>() + std::declval<T>() * std::declval<U>()) sum = 0;
  10.       for( std::size_t i = 0; i < lhs.size() && i < rhs.size(); ++i ) {
  11.       	sum += lhs[i] * rhs[i];
  12.       }
  13.       return sum;
  14.     }
  15.     template<typename LHS>
  16.     struct half_dot {
  17.       LHS lhs;
  18.       half_dot( LHS&& lhs_ ):lhs(std::forward<LHS>(lhs_)) {}
  19.       template<typename RHS>
  20.       decltype( dot_product( std::declval<LHS>(), std::declval<RHS>() ) )
  21.       operator*( RHS&& rhs ) const {
  22.         return dot_product( std::forward<LHS>(lhs), std::forward<RHS>(rhs) );
  23.       }
  24.     };
  25.     struct dot_t {};
  26.     template<typename LHS>
  27.     half_dot<LHS> operator*( LHS&& lhs, dot_t ) {
  28.       return {std::forward<LHS>(lhs)};
  29.     }
  30.     static dot_t dot;
  31.  
  32.     int main() {
  33.       std::vector<int> foo = {1,2,3};
  34.       std::vector<int> bar = {3,2,1};
  35.       std::cout << (foo *dot* bar) << "\n";
  36.     }
Success #stdin #stdout 0s 3472KB
comments (?)
stdin 
Standard input is empty
stdout 
10
https://ideone.com/C7lTn6
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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