Fernando Cacciola wrote:
David Abrahams wrote:
Anthony Williams <anthony_w.geo@yahoo.com> writes:
How's this for a radical thought --- optional<T> should not be assignable from T. That way, it doesn't matter whether T is a reference, or not.
There's at least some precedent for types that are "immutable except for copy assignment."
The assignment from T is really a kind of mutating operation.
Indeed. I'm leaning fast into dropping assignment form T. That definitely solves the reference binding issues.
Instead, to change the binding, use reset(), and to assign use *.
To make that valid for a null optional, I think operator* would have to return a proxy reference... which is not an altogether bad idea, IMO.
That would actually bring back the problem as assignment to a null reference would bind and then there's the question about what to do with assignment to a non-null reference (rebind as I proposed or not-rebind as Joel proposed) But if we do as both Sam Partignton and Antony Williams suggest, drop assignment from T altoghether, the situation looks a lot more clear, at least to me.
FWIW, I like the direction this is heading into. Dropping assignment from T altogether is a wise move! I wouldn't mind copy assignment and *explicit* construction. I wouldn't mind reset(T) too. IMO, that interface is orthogonal; and there's a clear precedent: shared_ptrs (which has both reset and copy assignment). Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net