On Fri, May 27, 2011 at 1:13 PM, Steven Watanabe <watanabesj@gmail.com>wrote:
On Fri, May 27, 2011 at 9:52 AM, Christian Holmquist <c.holmquist@gmail.com>wrote:
On 27 May 2011 11:28, Stewart, Robert <Robert.Stewart@sig.com> wrote:
Krzysztof Czainski wrote:
Vladimir Batov prepared a safebool helper class as part of his Pimpl library.
[snip]
There exists a safebool in already accepted Boost.Log:
I'll chime in for my vote of something more along the lines of Andrey's nullary macro design, except using a pointer-to-member-variable rather
a pointer-to-member-function to address MSVC efficiency concerns (see
On 05/27/2011 11:55 AM, Jeffrey Lee Hellrung, Jr. wrote: than prior
post by S.T. Lavavej). I use something like the following, which I had also picked up from Andrey in a past boost-dev list post.
#define BOOST_EXPLICIT_BOOL() \ private: \ struct _boost_explicit_bool_struct \ { int _dummy; int member; }; \ typedef int (_boost_explicit_bool_struct::*_boost_bool_type); \ public: \ operator _boost_bool_type() const { return !*this ? 0 : &_boost_explicit_bool_struct::member; }
When BOOST_NO_EXPLICIT_CONVERSION_OPERATORS is not defined, then the above macro is defined to just declare an explicit bool conversion, so it amounts to the same framework you would use in C++0x.
I prefer a macro solution over a CRTP solution because 1) it retains POD'ness (in C++03, at least; I believe the definition of POD has been extended in C++0x...?); and 2) the macro appears in the same place one would otherwise declare a bool conversion operator.
I also like the solution to use operator! by default in the implementation of the explicit bool conversion operator; perhaps a second macro could be provided to allow one to specify the specific expression (e.g., "!!*this" or "as_bool()") one should use.
What about a macro that can be used like
BOOST_EXPLICIT_BOOL_OPERATOR() const { return ...; }
Are you thinking something along the lines of #define BOOST_EXPLICIT_BOOL_OPERATOR() \ [...define a safe-bool operator that calls, e.g., _boost_as_bool() to determine true'ness...] \ bool _boost_as_bool() ? - Jeff