Hi Niels,
I'm normally against obscure functions that are meant to save a few keystrokes. OTOH, while the verbose alternative is perfectly clear and I wouldn't even consider searching for a shortcut, this particular shortcut looks clear enough to justify it.
So, Arno: don't you agree swap is better?
Would a function like optional<T>::swap_if_initialized(T&) indeed be the preferable one for Arno's use case? It isn't yet entirely clear to me, as it seems that Arno would like to have an implicit conversion, while passing the value from optional<T> to its target.
I actually didn't notice that the first time. Of course swap() can do the same via "optional<T>::swap_if_initialized(U&)" for that matter.
If so, does the swap() method really need the "_if_initialized"? I would just add overloads to the existing swap:
bool optional<T>::swap(T& a) bool swap( optional<T> const&x, T& y ) ; bool swap( T const&x, optional<T> const& y ) ;
I know 'swap' is a big name, but distorting it with a return value doesn't seem disruptive enough to justify choosing a different name.
Personally, I would prefer to have such functions named slightly different from "swap", to make clear that they're not regular swap function. You know, people expect a swap member function to /always/ successfully exchange the values, while swap_if_initialized would /only/ exchanges the values when optional<T> is "initialized" (non-empty).
OK, that's a very good argument.
But I wouldn't mind if it would be named differently, e.g., optional<T>::optional_swap(T&) :-)
I think I like this one better.
IMO a "swap-if-initialized" /member/ function might be especially useful because it allows swapping an rvalue (optionally).
Indeed.
I'm not sure if free "swap-if-initialized" function overloads would also be needed. What do you think?
As it won't be just swap(), it doesn't need to be a free function, and right now at least I can't see any reason for having it.
Anyway, the main question remains: will any of those "swap-if-initialized" functions be appreciated, or not...?
I do, so if no one points out a good reason for adding it, I will. As I said before I really hate bloated interfaces with this seems sufficiently useful and syntactically clear. Best -- Fernando Cacciola SciSoft Consulting http://www.scisoft-consulting.com