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  1. #include <tuple>
  2. #include <iostream>
  3. using namespace std;
  4.  
  5. typedef std::tuple<int,char,int> TupleType;
  6.  
  7. template<typename TupleT,typename OnElementHandler, size_t N>
  8. struct TupleIterator{    
  9.     static void call(const TupleT& tuple, OnElementHandler& OnElement){ 
  10.         auto nthElem = std::get<N>(tuple);
  11.         OnElement(nthElem);        
  12.         TupleIterator<TupleT,OnElementHandler,N-1>::call(tuple,OnElement);
  13.     }
  14. };
  15. template<typename TupleT,typename OnElementHandler>
  16. struct TupleIterator<TupleT,OnElementHandler,0>{  
  17.      static void call(const TupleT& tuple, OnElementHandler& OnElement){ 
  18.         auto firstElem = std::get<0>(tuple);        
  19.         OnElement(firstElem);
  20.     }
  21. };
  22. template<typename T1,typename T2>
  23. struct IsSame{enum{result = 0};};
  24.  
  25. template<typename T>
  26. struct IsSame<T,T>{ enum{result = 1}; };
  27.  
  28. template<typename T,size_t TargetCount, size_t BeginIndex, size_t EndIndex, typename Tuple>
  29. T getNthTypeReverse(const Tuple& t, const T& defaultValue = T()){
  30.     //assert 0 <= N <= tuple.size
  31.     T result = defaultValue;    
  32.     struct NthGrabber{
  33.        T& result;
  34.        const size_t n;
  35.        size_t count;
  36.        NthGrabber(T& r, const size_t n): result(r),n(n),count(0){}
  37.        void operator()(const int i){
  38.            if(IsSame<T,int>::result){
  39.                ++count;
  40.                if(count == n) result = i;
  41.            }
  42.  
  43.        }
  44.        void operator()(const char c){
  45.            if(IsSame<T,char>::result){
  46.                ++count;
  47.                if(count == n) result = c;
  48.            }
  49.        }
  50.        //overload for other version too...
  51.     }OnElement(result,TargetCount+1); //WILL update result if condition meet
  52.     const size_t tupleSize = EndIndex - BeginIndex;
  53.     TupleIterator<TupleType,NthGrabber,tupleSize>::call(t,OnElement); 
  54.     return result;
  55. }
  56. int main(){
  57.     TupleType t(10,'a',5);    
  58.     const size_t tupleSize = std::tuple_size<decltype(t)>::value - 1;
  59.     int lastInt = getNthTypeReverse<int,0,0,tupleSize,TupleType>(t,-1); 
  60.     int secondLastInt = getNthTypeReverse<int,1,0,tupleSize,TupleType>(t,-1); 
  61. 	int thirdLastInt = getNthTypeReverse<int,2,0,tupleSize,TupleType>(t,-1); 
  62.     cout << "lastInt = " << lastInt << endl;	
  63. 	cout << "SecondLast = " << secondLastInt << endl;
  64. 	cout << "ThirdLast = " << thirdLastInt << endl;
  65.  
  66. 	char lastChar = getNthTypeReverse<char,0,0,tupleSize,TupleType>(t,'\0'); 
  67. 	cout << "LastChar = "  << lastChar << endl;
  68.  
  69.     return 0;
  70. }
Success #stdin #stdout 0s 2896KB
comments (?)
stdin
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Standard input is empty
stdout
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lastInt = 5
SecondLast = 10
ThirdLast = -1
LastChar = a
https://ideone.com/Uk2JTC
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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