Steven Watanabe wrote:
I don't think that non-template friends should be defined inline in a class template because they are always supposed to be instantiated regardless of whether they are used or not (unlike ordinary members).
Thanks, Steven. Do I understand correctly that when you look at the following example, you find the definition of operator+ preferable to operator- ? ////////////////////////////////////////////////////////// template <typename> class safe_int; template <typename T> safe_int<T> operator+(safe_int<T>, safe_int<T>); template <typename T> class safe_int { public: friend safe_int operator+ <>(safe_int, safe_int); inline friend safe_int operator-(safe_int, safe_int) { throw "operator- not yet implemented."; } }; template <typename T> safe_int<T> operator+(safe_int<T>, safe_int<T>) { throw "operator+ not yet implemented."; } ////////////////////////////////////////////////////////// I still hesitate, because the non-template inline friend, operator-, appears to support implicit conversions more intuitively... I think. ////////////////////////////////////////////////////////// struct convertible_to_safe_int { operator safe_int<int>() const { return safe_int<int>(); } }; int main() { safe_int<int>() - convertible_to_safe_int(); // okay convertible_to_safe_int() - safe_int<int>(); // okay safe_int<int>() + convertible_to_safe_int(); // error convertible_to_safe_int() + safe_int<int>(); // error } ////////////////////////////////////////////////////////// Isn't support of such conversions (in a symmetrical way) the main reason to declare such operators as non-members, rather than as member functions? Kind regards, Niels -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center