Jeffrey Lee Hellrung, Jr. skrev:
However, it appears Thorsten's implementation creates a null_guard if the condition *is* true (the boolean is named "is_null", after all). I'd consider Joaquin's semantics to be less confusing.
Oh, I overlooked that. I simple did what felt most natural from a usage perspective, to avoid negating the constant. AFAICT, this the most common usage scenario. Thus when I see make_guard_if<boost::has_nothrow_copy<T>::value>( ... ) I don't read the _if alone (as part of what is being returned), but I read the whole make_guard_if<> as a tool that generates guards as needed depending on has_nothrow_copy<>. Joaquin, what is your take on this?
Also, since I'm here, perhaps you should have a make_obj_guard_if_c taking the boolean template parameter, while make_obj_guard_if takes a Boost.MPL boolean constant class. This is the convention used by Boost.EnableIf and Boost.MPL (among other Boost libraries), right?
The if_c<> code is usually pure meta code which is not the case here. -Thorsten