Re: [Boost-users] mpl::fold problems

Zitat von sergey kostanbaev :

template struct tr_field2 { static const unsigned count = space; }

typedef boost::mpl::vector4< tr_field2, tr_field2, tr_field2, tr_field2

...

Test_description;

I want to calculate a sum of all tr_field2::count I've read in the docs mpl::fold is for the case.

I tried to compose

typedef boost::mpl::fold, boost::mpl::plus >

...

::type fcount;

but it won't compile. It seems I misundestood something.

template<typename T> struct get_count{ typedef mpl::int_ type; }; typedef boost::mpl::fold, boost::mpl::plusmpl::_2 >

::type fcount;

the placeholders are not evaluated by mpl::_::count. and mpl::plus expects a mpl integral constant, not a value.