It seems like different Boost libraries use different nullable types. * Optional uses boost::none * Tribool uses boost::logic::indeterminate_keyword_t * Tuple uses boost::tuples::null_type * Variant uses boost::blank And there are possibly more. What are your opinions about unifying these?
Though there is some difference between null and void, MPL provides a void type. http://www.boost.org/doc/libs/1_54_0/libs/mpl/doc/refmanual/void.html I think there may also be some type "na" or something to that effect used to fill empty elements of a sequence to work around the lack of variadic templates in C++03, but I couldn't find the exact reference in a cursory search. Cheers! Andrew Hundt On Sat, Jul 13, 2013 at 7:56 AM, Bjorn Reese <breese@mail1.stofanet.dk>wrote:
It seems like different Boost libraries use different nullable types.
* Optional uses boost::none * Tribool uses boost::logic::indeterminate_**keyword_t * Tuple uses boost::tuples::null_type * Variant uses boost::blank
And there are possibly more.
What are your opinions about unifying these?
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The std::optional proposed for C++14 uses std::nullopt and it was purposely kept separate from any other nulls because of implicit conversion. If you put a tribool into a optional then set it to some_common_null, are you setting the optional to null/disengaged or setting the tribool to indeterminate (and the optional is thus engaged). ie: optional<tribool> op = some_null; Sure an optional tribool is odd (in effect a quadbool) but probably will happen somewhere, and not obvious if it happens in templates... Tony Sent from my portable Analytical Engine ------------------------------ *From:* "Bjorn Reese" <breese@mail1.stofanet.dk> *To:* "boost@lists.boost.org" <boost@lists.boost.org> *Sent:* 13 July, 2013 8:58 AM *Subject:* [boost] Nullable types It seems like different Boost libraries use different nullable types. * Optional uses boost::none * Tribool uses boost::logic::indeterminate_keyword_t * Tuple uses boost::tuples::null_type * Variant uses boost::blank And there are possibly more. What are your opinions about unifying these? _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
On 13-07-2013 13:56, Bjorn Reese wrote:
It seems like different Boost libraries use different nullable types.
* Optional uses boost::none * Tribool uses boost::logic::indeterminate_keyword_t * Tuple uses boost::tuples::null_type * Variant uses boost::blank
And there are possibly more.
boost::nullable<T> from Boost.PtrContainer. -Thorsten
participants (4)
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Andrew Hundt -
Bjorn Reese -
Gottlob Frege -
Thorsten Ottosen