Hello everybody, A couple of weeks ago I initiated the discussion about simple typeof emulation, and provided an example on how it can be done with the help of MPL vector of integral constants. I then used MS-specific __COUNTER__ macro to spare the user from specifying the unique integer for each registered class/template. I hoped to find a way to do something similar in standard C++, and asked preprocessor experts for help. Indeed, Paul Mensonides suggested such a way. At first I thought that it will not be good enough replacement for the __COUNTER__, but then I realized that I was wrong. So I re-worked my implementation of typeof, and now offerring it to your attention. Besides removing __COUNTER__, I used the Boost.Preprocessor library to cleanup the implementation. Also, after the discussion with Jody Hagins, I put the encoding/decoding classes inside anonimous namespace to avoid collisions between translation units. The provided example shows what registration needs to be done to calculate the type of a lambda functor: #include BOOST_TYPEOF_BEGIN_REGISTRATION() BOOST_TYPEOF_REGISTER_TEMPLATE(tuples::tuple, 2); BOOST_TYPEOF_REGISTER_TEMPLATE(lambda_functor, 1); BOOST_TYPEOF_REGISTER_TEMPLATE(lambda_functor_base, 2); BOOST_TYPEOF_REGISTER_TEMPLATE(relational_action, 1); BOOST_TYPEOF_REGISTER_TEMPLATE(logical_action, 1); BOOST_TYPEOF_REGISTER_TYPE(greater_action); BOOST_TYPEOF_REGISTER_TYPE(less_action); BOOST_TYPEOF_REGISTER_TYPE(and_action); BOOST_TYPEOF_REGISTER_TYPE(placeholder<1>); BOOST_TYPEOF_REGISTER_TYPE(placeholder<2>); #include BOOST_TYPEOF_END_REGISTRATION() main() { BOOST_TYPEOF_ALLOCATE(fun, _1 > 15 && _2 < 20); // <unspecified> fun(_1
15 && _2 < 20); int n = 19; assert(fun(n, n)); }
One of remaining problems is inability to process top-level consts and references, that get eatten up at the function level, before the partial template specialization gets involved... Although I believe that I don't do anything non-standard now, unfortunately I can't prove it myself. The only compiler I have besides MSVC is GCC, and it gives me "sorry not implemented" on something as simple as mpl::int_<sizeof(foo(...))>... Besides, GCC already has a typeof. Would anybody be so kind as to try the "typeof" with some other compiler? I would really apprciate this... Here is the link: http://groups.yahoo.com/group/boost/files/typeof.zip Any comments are greatly appreciated. Thanks, Arkadiy