#include <iostream>


using namespace std ;

//This function determines if something
//is lvalue or rvalue
template <typename T>
constexpr bool is_lvalue(T&&) {
  return std::is_lvalue_reference<T>{};
}



//LVALUE REFERENCE
void function1LValueRef( int& a1 )
{
   cout << "function1:" << a1 << endl ;
}

//RVALUE REFERENCE
void function2RValueRef( int&& a1 )
{
  //Since a1 is a name it is a lvalue at this point inside the
  //function but the function can only take rvalues.
  cout << "Is a1 a lvalue: " << is_lvalue( a1 ) << endl ;
  //a1 = 25 ;
}


int main()
{
   int x1 = 10 ;
   int y1 = 30 ;


   //Need to initialize references
   int&& x2R = 20 ;
   int&& x3R = 30 ;
   int& x3L = x1  ;

   //compiler error
   //A rvalue reference must be initialized
   //int&& x7  ;
   //Can only initialize it with a temporary object
   // int&& x7 = x1  ;

   //can reassign values to r reference
   //x2R is not pointing to x3R but rather it's
   //value is being updated.
   x2R = x3R ;
   cout << "x2R:" << x2R << endl ;
   x2R = 35 ;
   cout << "x2R:" << x2R << endl ;
   //Can initialize l-value reference with r-value
   //reference. Anything that has a name is l-value.
   int& x6R = x2R ;

   //cannot initialize lvalue
   //reference with a constant/rvalue
   //At the point of definition
   //int& x8 = 25 ;
   //can do
   //const int& x1 = 20 ;

   //Can only initialize rvalue reference with
   // rvalues
   //int&& x7 = x3L ;



   function1LValueRef( x1 ) ;
   function2RValueRef(  20 ) ;


   //Allowed
   //
   x2R = x1 ;
   x2R = 40 ;   //reassignment to a r value reference

   cout << "x2R:" << x2R << endl ;
   //Not a reassignment of the lvalue reference.
   //changes the value of x1 and  x3L "points" to x1 .
   x3L = y1 ;

   //x2R's value is being set to x1
   x1 = x2R ;
   cout << "x1:" << x1 << endl ;


   //function 2 is r reference
   //Compiler error r-value reference expects a constant
   //  function2RValueRef(  x1  ) ;

    //ok move converts a l value to a r value
   function2RValueRef( move(x1)  ) ;



    //x2R is a name so it's a l value at this point
   function1LValueRef( x2R ) ;


    cout << "Is x2R a lvalue: " << is_lvalue( x2R ) << endl ;
    cout << "Is 12 a lvalue: " << is_lvalue( 12 ) << endl ;


    function2RValueRef(  move(x2R)   ) ;
    cout << "x2R value: " << x2R << endl ;
    //compiler error even though x2R is rvalue !!!
    //But it has a name so now is lvalue !!
    // function2RValueRef(  x2R   ) ;
    function2RValueRef( 21 ) ;

     int x19 = 5 ;
     cout << x19 << " " << move(x19) << endl ;

   return 0 ;
}