2009/10/20 Beman Dawes <bdawes@acm.org>:

One particular concern is that as currently worded, the N2838 proposal requires throws() return a null reference, which they see as relying on undefined behavior.

So it sounds like the idea solution is something that looks like a reference to the caller, for shortness of typing, but looks like a pointer to the implementation, to ease checking and avoid the weirdness of null references. struct optional_error_code_ref { optional_error_code_ref() : p_() {} optional_error_code_ref(optional_error_code_ref const &ecr) : p_(ecr.p_) {} optional_error_code_ref(error_code &r) : p_(&r) {} error_code &operator*() const { return *p_; } error_code *operator->() const { return p_; } operator safe_bool() const { return safe_bool(p_); } private: error_code *p_; }; Then the call is done the same was as before: error_code ec; foo(ec); But it's obvious to check, and never deals in null references: void foo(optional_error_code_ref ec = optional_error_code_ref()) { ... if (ec) { ec->value = bar; } else { throw bar_exception(); } ... } It would of course be better spelt qux<error_code&>, but I'm not sure exactly what name that should be. ~ Scott (Hopefully the subject change will get us out of the exceptions vs error codes quagmire.)