On 1 September 2011 04:28, Mostafa <mostafa_working_away@yahoo.com> wrote:
I see the same thing as all of the other cases, the "exactly 1 time" is relaxed into "0 or more times".
Ahh, I disagree with that.
That may be, but you haven't shown a flaw in my reasoning. I contend that in the normal lifetime window, both objects and references exist "exactly 1 time". Where is that reasoning inconsistent?
IMO, if maybereff was not bound at construction time, then it should always remain "uninitialized".
You are arguing for "at most once where lifetime begins at the point of construction of the optional<U&>"? Why not argue the same for objects? I don't see the difference, other than you want to introduce a difference.
Now Fernando has made an interesting case for why disallowing the assignment operator for optional<T&> and allowing it for all other types is bad.
He is arguing for consistency. So am I. Construction/assignment of an optional<T> is for affecting the lifetime of the underlying T object it holds. Assignment doesn't affect lifetime of C++ objects or references, so if one is going to use that syntax for optional<T>, one has to define what the semantics should be in both the case where the underlying object or reference does not yet exist and in the case where the underlying object or reference already exists. Assignment to an optional<T> almost models destroying the underlying T object (if it already exists) followed by creating a new underlying object. In the case of objects, it performs an optimization by using assignment instead of destroy/construct in the case where the object already exists (which is why I said "almost models" in the previous statement). That optimization does not exist for references. -- Nevin ":-)" Liber <mailto:nevin@eviloverlord.com> (847) 691-1404