longest template

#include <iostream>
#include <string>
//degenerate case
template<typename T>
T& longest(T& a)  {return a;}

// regular case
template<typename T>
 T& longest( T& a, T& b)
  {
    std::string A(a);
    std::string B(b);
    return (A.length() >= B.length())? a: b;
  }

// works for std:string, not for "string"
template<typename T, typename... Args>
T& longest( Args... args )
{
  return longest(  args...) ;
}



int main ( int argc, char* argv[])
{
  std::string a , b, c, d;

  a = "a";
  b = "ab";
  c = "abc";
  d = "abcd";

  std::string x = longest( a, b, c, d); // works fine

/* error
    longest.cpp:66:19: note: in instantiation of function template specialization
    'longest<char const[2], const char *, const char *, const char *>' requested here
*/
  std::string y = longest( "1" , "22", "333", "4444"); // why are different types? Remedy?

  std::cout << x << std::endl;
  std::cout << y << std::endl;

  return 0;
}