C++ debugging output

I like to write debugging information to an ostream instead of calling a logging function.

 retry:
  if (write(_fd, request.buffer(), request.length()) != request.length()) {
    if (errno == EAGAIN) {
     _debug << "retry" << endl;
      goto retry;
    }
    throw system_error(errno, generic_category(), "Could not write to serial port");
  }

By default, I don’t want to see debugging information, so I initialize my debugging ostream to a stream that sinks all data written to it:

#pragma once

#include <iostream>

class nullstream : public std::ostream {
public:
  nullstream() : std::ostream(nullptr) {}
  nullstream(const nullstream &) : std::ostream(nullptr) {}
};

template <class T>
const nullstream &operator<<(nullstream &&os, const T &value) { 
  return os;
}

I can then set the ostream to cerr or another stream if I want to see the debugging information. A downside of the approach is that the debug information will be formatted even if not debugging, so it is not suitable for high performance code.

I found this solution in a StackOverflow answer.