On 01/11/13 00:17, Joel de Guzman wrote:
On 1/11/13 2:00 PM, Larry Evans wrote:
On 01/10/13 21:38, Rob Stewart wrote: [snip]
Validity depends upon the class in question. A smart pointer can be null and still valid. In your case, the class has the semantics that it always references a value. Changing that, to permit a null state, may be acceptable or it may have unacceptable side effects. Perhaps a new type, with the null state, can be added and used in some of the current contexts.
The "truly tagged" variant here:
http://svn.boost.org/svn/boost/sandbox/variadic_templates/boost/composite_st...
has such a null state. When constructed with no arguments, it's in this null state. It's "truly tagged" because there can be duplicate bounded types distinguished only by the tag value. IOW, although:
Larry, sorry, but that's irrelevant. We are talking about recursive_wrapper here, not variant.
Regards,
OK, I probably was jumping to conclusions, but from looking at: http://www.boost.org/doc/libs/1_52_0/doc/html/variant/tutorial.html#variant.... which contained: typedef boost::variant< int , boost::recursive_wrapper< binary_op<add> > , boost::recursive_wrapper< binary_op<sub> > > expression; I concluded that recursive_wrapper always occurred in a variant. I further jumped to the conclusion that *if* the variant had a null state, then it would not assume any of its bounded types were "in effect"; hence, would not call any destructors for any bounded type or perform any operations on any bounded type; hence, the pointer in recursive wrapper would not even need to be zeroed because the containing variant would not assume that it even had a recursive_wrapper as one of its bounded types. Sorry if I misunderstood, but it seemed reasonable suggestion at the time. -regards, Larry