tribool doesn't play well with auto

[xiao-feng]

This prints "Not true.":

  tribool b = indeterminate;
  if(b) {
      cout << boolalpha << b << endl;
  }
  else {
      cout << "Not true." << endl;
  }

This prints "indeterminate":

  auto b = indeterminate;
  if(b) {
      cout << boolalpha << b << endl;
  }
  else {
      cout << "Not true." << endl;
  }

Is it a bug? Or is it expected behavior? What's the rationale?

Thanks!

[u8cat]

That's because indeterminate is a function:

// Check if the given tribool has an indeterminate value. Also doubles as a
// keyword for the 'indeterminate' value
BOOST_CONSTEXPR inline bool indeterminate(tribool x, detail::indeterminate_t) BOOST_NOEXCEPT
{
  return x.value == tribool::indeterminate_value;
}

Therefore, b is a pointer to the function, which will never be nullptr.