operator bool takes precedence over ostream after 6.1

[timblechmann]

class Symbol
{
public:
  string string() const { return m_string; }
  operator bool() const { return !m_string.empty(); }

private:
  std::string m_string {"test"};
};

ostream& operator<< (ostream& os, const Symbol& symbol)
{
    os << symbol.string();
    return os;
}

the implicit bool conversion confuses fmt:

• 6.0: format / sprintf give "test"
• 6.1: format gives "true, sprintf gives "test"
• 6.2: format / sprintf give "true"

my coworker came up with this reproducer on godbolt: https://godbolt.org/z/ffGf49W43

[vitaut]

Unfortunately there is no good way to handle ambiguous cases like this. You can provide an formatter specialization to suppress the implicit conversion.

[timblechmann]

unfortunately the custom formatter is only applied with fmt::format, not with fmt::sprintf

[vitaut]

sprintf is mostly for migrating legacy code and doesn't support ostreams or other extension mechanisms.