在C++中实现LINQ

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#include 
  
   
#include 
   
     template
    
      struct from_range { typedef typename std::iterator_traits
     
      ::value_type value_type; TIterator current, upcoming, end; from_range(TIterator begin, TIterator end) : current(begin), upcoming(begin), end(end) {} template
      
        decltype(auto) operator>>(TRangeBuilder builder) const { return builder.build(*this); } decltype(auto) front() const { return *current; } bool next() { return upcoming == end ? false : (current = upcoming++, true); } }; template
       
         struct where_range { typedef typename TRange::value_type value_type; TRange range; TPredicate predicate; where_range(TRange range, TPredicate predicate) : range(range), predicate(predicate) {} template
        
          decltype(auto) operator>>(TRangeBuilder builder) const { return builder.build(*this); } decltype(auto) front() const { return range.front(); } bool next() { while(range.next()) if(predicate(range.front())) return true; return false; } }; template
         
           struct where_builder { TPredicate predicate; where_builder(TPredicate predicate) : predicate(predicate) {} template
          
            auto build(TRange range){ return where_range
           
            (range, predicate); } }; struct to_vector_builder { template
            
              auto build(TRange range){ std::vector
             
               result; while(range.next()) result.push_back(range.front()); return result; } }; template
              
                auto from(TContainer const& container) { return from_range
               
                (std::begin(container), std::end(container)); } auto to_vector() { return to_vector_builder(); } template
                
                  auto where(TPredicate predicate) { return where_builder
                 
                  (predicate); } int main() { int a[] = {1, 2, 3, 4}; auto v = from(a) >> where([](int n){return n % 2 == 0;}) >> to_vector(); for(int i : v) std::cout << i << std::endl; } /* 2 4 */ 
                 
                
               
              
             
            
           
          
         
        
       
      
     
    
   
  

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