Roman Perepelitsa writes:

2009/5/6 Roman Perepelitsa It's less efficient, because all arguments will be copied. It's also more

typing, longer compilation times and more code generated. 

There is one more caveat. This approach does not work with polymorphic types

(you'll get slicing). I don't think there are any advantages in passing boost::optional<T> compared to const T*.Roman Perepelitsa.

Thanks for the answer! Is there a way to avoid the copy (and thus the slicing)? Perhaps using boost::optional or boost::optional< boost::reference_wrapper<T> > ?

On Wed, May 6, 2009 at 4:44 AM, Gevorg Voskanyan wrote:

Igor R wrote:

...

...

f(p1, boost::optional<Param2>(p2), boost::optional<Param3>(), boost::optional<Param4>(p4) );

The params would be implicitly converted, so you can call like this: f(p1, p2, boost::optional<Param3>(), p4);

boost::none will be helpful as well: f(p1, p2, boost::none, p4);

Beside the headers, Google doesn't yield documentation on boost::none. Could someone please explain it's intended use? I see none_t is a typedef to a member of none_helper, a struct with no members, and none is a const none_t, but I'd expect such a pointer to not be convertible to anything, so I'm not following on passing boost::none to a boost::optional as above, nor can't figure out the use for none. Can someone please provide some details / background info on none? Thanks, --DD

Dominique Devienne wrote:

...

boost::none will be helpful as well: f(p1, p2, boost::none, p4);

Beside the headers, Google doesn't yield documentation on boost::none.

Could someone please explain it's intended use? I see none_t is a typedef to a member of none_helper, a struct with no members, and none is a const none_t, but I'd expect such a pointer to not be convertible to anything, so I'm not following on passing boost::none to a boost::optional as above, nor can't figure out the use for none. Can someone please provide some details / background info on none? Thanks, --DD

This is described in the documentation of boost.optional, here: http://www.boost.org/doc/libs/1_39_0/libs/optional/doc/html/boost_optional/d... Best Regards, Gevorg