Mat Marcus <mmarcus-boost@[...].org>  wrote in message
news:318546735.1063785477@[...]..
> 
> 
>  --On Tuesday, September 09, 2003 6:43 PM -0300 Fernando Cacciola
>  <fernando_cacciola@[...].com> wrote:
> 
>  > Hi boosters,
>  >
>  > Following the suggestions that had been made since Optional's
>  > acceptance I've updated the library.
>  > I will upload the new version on main CVS tomorrow noon unless
>  > someone objects.
> 
>  Thanks a lot for updating optional! The new version really simplifies
>  my optional usage to the point where I'm willing to commit to it in my
>  current project.
> 
Great!

Thanks for your feedback!

>  [snip]
> 
>  This is rather convenient. It is a little bit less convenient to
>  construct the end out_edge_iterator. In my case end is represented by
>  an iterator with uninitialized optional state. Here I apparently have
>  to write:
> 
>  out_edge_iterator i(optional<out_edge_iterator>());
>  file://longer in its fully qualified glory
> 
I think the line above should probably be:

out_edge_iterator i(optional<edge_descriptor> ());

>  I imagine that it could be useful to have something like a universal
>  'none' object that could be passed to functions expecting optionals. I
>  would expect its effect to be the same as passing the anonymously
>  constructed optional in the line of code directly above. That is I
>  would like to write:
> 
>  out_edge_iterator end(none); file://optional::none?
> 
Well, something like this can be done, though I wonder why couldn't
you just use the default constructor as in:

out_edge_iterator end;

which is the cannonical way to introduce an uninitialized optional<> .

> 
>     * Safe optional<bool>'s as tri-bools would be quite useful to me. I
>  personally would sacrifice the convenience of testing without using
>  is_initialized() to gain tri-bools but I don't want to cover old
>  territory. Perhaps there's some other way of making optional<bool>'s
>  safer to use. What would you think of, say, using enable_if (or better
>  disable_if) to disable implicit bool conversion and operator! for when
>  T == bool (or when T already is_convertible to bool)?
> 
I decided not to treat optional<bool>  specially since as Doug just said
there is boost::tribool.
In order to use optional "safely" and uniformly in the presence of
[T=possibly bool] all you have to do is not to use the safe_bool feature.
For instance, you can consistently use the double-bang idiom:

if ( !!opt ) ....

HTH

Fernando Cacciola




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