Andreas Pokorny wrote:
On Fri, Dec 02, 2005 at 12:11:32PM -0800, Eric Niebler <eric@boost-consulting.com> wrote:
Andreas Pokorny wrote:
Hi, The default implementation of boost::fusion::pair<first,second> only stores an instance of second. I might need a fusion::pair which does not store that instance either,
If you want a map with *no* runtime data, then you should use mpl::map<>, not fusion::map<>. mpl::map<> uses mpl::pair<>, which has no runtime data. (Caveat: mpl::map is broken in more than one respect at the moment. Hopefully, it'll be fixed soon.)
Ah, I could write an interleaved map that splits the pair sequence into runtime and compile time info holders.
I'm not sure I follow, but if my suggestion led you to a solution, I'm happy to take the credit. ;-)
How is mpl::map broken?
mpl::map doesn't guarantee unique keys at the moment. For instance, this doesn't work. typedef mpl::insert<mpl::map0<>, mpl::pair<int, float> >::type t1; typedef mpl::insert<t1, mpl::pair<int, double> >::type t2; // Oops, this assertion fails BOOST_MPL_ASSERT_RELATION(mpl::size<t2>::value, ==, 1); After the two insertions, the map contains pair<int,float> and pair<int,double>, but AFAICT it should only contain mpl::pair<int, float>. Also, mpl::insert_range does not work with mpl::map<> even though the docs say it should. Also, I have found places where using an mpl::map<> fails where using mpl::map0<> works. Ditto for mpl::set<> and mpl::set0<>. If you decide to go this route, be aware, or else wait for the fixes. -- Eric Niebler Boost Consulting www.boost-consulting.com