On 02/15/09 13:29, Steven Watanabe wrote:
AMDG
Larry Evans wrote:
This "optimization" was ineffective. There were 303 instantiations vs. the 297 in the original version :( .
Changing equal to is_same (and making adjustments to where ::type is placed) resulted in just 185 instantiations!
If you really must optimize this to death...
Well, the mpl and fusion people have spent a lot of effort on it; so, I figure it must be worth while.
#include <boost/mpl/next.hpp> #include <boost/mpl/deref.hpp> #include <boost/mpl/begin.hpp> #include <boost/mpl/end.hpp> #include <boost/mpl/and.hpp> /* Calculate the mpl::and_ of a sequence of nullary logical metafunctions.*/ template<class Begin, class End> struct and_iter : boost::mpl::and_< typename boost::mpl::deref<Begin>::type, and_iter<typename boost::mpl::next<Begin>::type, End>
{};
template<class End> struct and_iter<End, End> : boost::mpl::false_ {};
template <typename Seq> struct and_seq : and_iter<typename boost::mpl::begin<Seq>::type, typename boost::mpl::end<Seq>::type> {};
So, in summary, the and_ifops::if_ test has been replaced with the and_iter specialization of <End, End>, and the laziness is achieved by use of and_; however, why not just use eval_if to achieve the laziness: -{--and_seq_eval_if_iter.cpp-- #include <boost/mpl/next.hpp> #include <boost/mpl/deref.hpp> #include <boost/mpl/begin.hpp> #include <boost/mpl/end.hpp> #include <boost/mpl/eval_if.hpp> /* Calculate the mpl::and_ of a sequence of nullary logical metafunctions.*/ template<class Begin, class End> struct and_iter : boost::mpl::eval_if_< typename boost::mpl::deref<Begin>::type, and_iter<typename boost::mpl::next<Begin>::type, End>, boost::mpl::false_
{};
template<class End> struct and_iter<End, End> : boost::mpl::false_ {}; template <typename Seq> struct and_seq : and_iter<typename boost::mpl::begin<Seq>::type, typename boost::mpl::end<Seq>::type> {}; #include <and_seq_instances.hpp> -{--end_seq_eval_if_iter.cpp-- This shaved off a few instantiations (128 vs. 163 on my machine). BTW, Steven, do you know how to get timing? I've tried the following but nothing is output: #the following modelled after time-rule from: # # http://beta.boost.org/doc/tools/jam/jam/language.html#jam.language.variables... # rule timing-rule ( args * : target : start end user system ) { echo $(start) $(end) ; } #the following modelling on: # # http://www.boost.org/doc/tools/jam/jam/language.html#jam.language.variables # __TIMING_RULE__ on and_seq_while-time = timing-rule ; compile and_seq_while.cpp : <include>. <link>static : and_seq_while-time ;