gimpxx で三項演算子が爆発した

gistfile1.cpp

// gmpxx : mpz_class で三項演算子が使えない（解決した）
#include <iostream>
#include <gmpxx.h>

// これなら OK
// mpz_class next_collatz(const mpz_class &n){
//   if(n % 2 == 0){
//     return n >> 1;  
//   }else{
//     return n * 3 + 1;
//   }
// }

//これだとコンパイルエラー (compile error)
// mpz_class next_collatz(const mpz_class &n){
//   return n % 2 == 0 ?  n >> 1 : n * 3 + 1;
// }

//これで通った OK
mpz_class next_collatz(const mpz_class &n){
  return n % 2 == 0 ?  mpz_class(n >> 1) : mpz_class(n * 3 + 1);
}

int main(int argc, char**argv){
  if(argc<2) return -1;
  mpz_class n(argv[1]);
  for( ;n!=1; n = next_collatz(n)) std::cout << n << " ";
  std::cout << n << std::endl;
  return 0;
}

/*
$gcc -v
gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5) 

$gcc collatz.cpp -o collatz -lgmpxx
collatz.cpp: In function ‘mpz_class next_collatz(const mpz_class&)’:
collatz.cpp:13: error: no match for ternary ‘operator?:’ in ‘operator== [with T = __mpz_struct [1], U = __gmp_binary_expr<__gmp_expr<__mpz_struct [1], __mpz_struct [1]>, long int, __gmp_binary_modulus>](((const __gmp_expr<__mpz_struct [1], __gmp_binary_expr<__gmp_expr<__mpz_struct [1], __mpz_struct [1]>, long int, __gmp_binary_modulus> >&)((const __gmp_expr<__mpz_struct [1], __gmp_binary_expr<__gmp_expr<__mpz_struct [1], __mpz_struct [1]>, long int, __gmp_binary_modulus> >*)(& operator% [with T = __mpz_struct [1], U = __mpz_struct [1]](((const __gmp_expr<__mpz_struct [1], __mpz_struct [1]>&)((const mpz_class*)n)), 2)))), 0) ? operator>> [with T = __mpz_struct [1], U = __mpz_struct [1]](((const __gmp_expr<__mpz_struct [1], __mpz_struct [1]>&)((const mpz_class*)n)), 1ul) : operator+ [with T = __mpz_struct [1], U = __gmp_binary_expr<__gmp_expr<__mpz_struct [1], __mpz_struct [1]>, long int, __gmp_binary_multiplies>](((const __gmp_expr<__mpz_struct [1], __gmp_binary_expr<__gmp_expr<__mpz_struct [1], __mpz_struct [1]>, long int, __gmp_binary_multiplies> >&)((const __gmp_expr<__mpz_struct [1], __gmp_binary_expr<__gmp_expr<__mpz_struct [1], __mpz_struct [1]>, long int, __gmp_binary_multiplies> >*)(& operator* [with T = __mpz_struct [1], U = __mpz_struct [1]](((const __gmp_expr<__mpz_struct [1], __mpz_struct [1]>&)((const mpz_class*)n)), 3)))), 1)’

Compilation exited abnormally with code 1 at Sun Oct 16 10:24:51
*/