On Mon, Aug 4, 2008 at 12:48 PM, Steven Watanabe <watanabesj@gmail.com> wrote:
AMDG
Emil Dotchevski wrote:
Also, I am not necessarily advocating strong exception guarantee. I would be fine if the semantics of operator= were such that it may leave the object in a particular unusual state. The problem is that as it is now, it may leave the object in a seemingly OK state.
Yes, I was aware of this workaround and of the one Mathias mentioned.
However, variant<foo,bar,blank> and variant<wrapper<foo>,wrapper<bar>> aren't the same as variant<foo,bar>. I'm questioning the rationale of the current variant::operator= semantics, not necessarily looking for a way to work around them.
It doesn't seem unreasonable to require boost::blank to be listed, in order to allow a variant to be left in a "particular unusual state"
It depends on the viewpoint. If you have operator= which may change the type of the stored value, it's quite reasonable to specify that if you list boost::blank as a valid type, it will be preferred over the other valid types. This still doesn't mean that it is desirable for operator= to be allowed to change the type of the stored object. If you list boost::blank as a valid variant, then there's nothing unusual about this state. The difference in meaning is subtle but nevertheless important: it's similar to a pointer that may legally be null, requiring the user to deal with this possibility, vs. a pointer which can never be null, allowing the user to assert when it is. Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode