On Friday 09 February 2007 08:55 pm, Timmo Stange wrote:
Frank Mori Hess wrote:
The problem is that we don't get to return an optional, because the return type is specified as "T", not "optional<T>". And, unfortunately, we can't rely on there always being a default constructor there.
Right now, the implementation is allowed to crash if you call one of these signals and there are no slots. Throwing an exception brings some sane defined behavior to something that is now completely undefined.
If we could reliably detect default-constructibility, we might be able to come up with something better.
We could add a little header with a definition of a "last_optional" combiner for people to use if they prefer.
Yes, that'd be nice. I think a non-throwing partial specialization (or a simulated one for compilers that don't support it) of last_value would be good.
If I'm following, you're saying something like last_value<T, U=T> would be like the current last_value<T> and last_value<T, optional<T> > would be like last_optional<T>? It seems easier just to provide a stand-alone last_optional<T> since the implementation of last_value<T> is so trivial. -- Frank