On Sat, May 28, 2011 at 6:22 AM, Krzysztof Czainski <1czajnik@gmail.com>wrote:
Thank you all for such large input ;-)
So the way I see it, most of us agree it would be nice to see one official safe-bool implementation tool in boost.
The first question is: should it be a CRTP class, or should it be a macro, or both perhaps?
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Macro usage: BOOST_EXPLICIT_BOOL_OPERATOR() const { return ...; }
I'm not sure how the macro would be implemented, but we'll get to that once we make the choice.
Right now I feel convinced to the macro version.
Here's a trial attempt at an implementation of the macro (warning: not tested): #ifndef BOOST_NO_EXPLICIT_CONVERSION_OPERATORS #define BOOST_EXPLICIT_OPERATOR_BOOL() \ explicit operator bool() #else // #ifndef BOOST_NO_EXPLICIT_CONVERSION_OPERATORS #ifndef BOOST_NO_EXPLICIT_OPERATOR_BOOL #define BOOST_EXPLICIT_OPERATOR_BOOL() \ struct _boost_explicit_operator_bool_struct { int _dummy; int member; }; \ typedef int (_boost_explicit_operator_bool_struct::*_boost_explicit_operator_bool_type); \ operator _boost_explicit_operator_bool_type() const \ { return _boost_explicit_operator_bool_impl() ? &_boost_explicit_operator_bool_struct::member : 0; } \ bool _boost_explicit_operator_bool_impl() #else // #ifndef BOOST_NO_EXPLICIT_OPERATOR_BOOL #define BOOST_EXPLICIT_OPERATOR_BOOL() \ operator bool() #endif // #ifndef BOOST_NO_EXPLICIT_OPERATOR_BOOL #endif // #ifndef BOOST_NO_EXPLICIT_CONVERSION_OPERATORS ...and we can, optionally, give _boost_explicit_operator_bool_struct and _boost_explicit_operator_bool_type private access, but I don't see a way to give _boost_explicit_operator_bool_impl private access, so the point might be moot. - Jeff