#include <iostream>
#include <vector>


using namespace std ;



//--------------------------------------------------------

template<typename MyVector, typename Index>    // works, but
auto function1(MyVector& c1, Index i1)       // requires
  -> decltype( c1[i1] )
  {
	  return c1[i1] ;
  }

template<typename MyVector, typename Index>    // works, but
auto function2(MyVector& c1, Index i1)       // requires
  {
	  return c1[i1] ;
  }

template<typename MyVector, typename Index>    // works, but
auto& function2a(MyVector& c1, Index i1)       // requires
  {
	  return c1[i1] ;
  }


template<typename MyVector, typename Index>    // works, but
decltype(auto) function3(MyVector& c1, Index i1)       // requires
  {
	  return c1[i1] ;
  }

//--------------------------------------------------------


int main()
{
  vector<int> v1 ;
  v1.push_back( 100 ) ;
  v1.push_back( 101 ) ;

  cout << "function1( v1, 0 ) " << function1( v1, 0 ) << endl  ;
  function1( v1, 0 ) = 101 ; //valid

  cout << "function2( v1, 0 ) " << function2( v1, 0 ) << endl  ;
  //function2( v1, 0 ) = 101 ; //invalid
  //auto by itself takes out the reference
  function2a( v1, 0 ) = 102 ; //valid

  cout << "function3( v1, 0 ) " <<  function3( v1, 0 ) << endl  ;
  function3( v1, 0 ) = 101 ; //valid


 return 0 ;
}


//--------------------------------------------------------