Re: [boost] [mpl] multiset

On 3/12/2015 7:48 PM, Eric Niebler wrote:

The metafunctions in meta::lazy don't assume their arguments are themselves lazy metafunctions, which would make lazy metafunction composition difficult. It's really just not the Meta way.

FWIW, I decided this was a legitimate shortcoming of Meta's approach, so I changed it. Now when you access the nested ::type of a lazy:: computation, it evaluates all nested lazy:: computations[*]. That makes composition much nicer. For instance: template<typename N> struct factorial : eval< if_c, lazy::multiplies>>> {}; This behaves differently than MPL[11]. Rather than passing a thunk representing dec<N> to factorial, lazy::dec<N> gets fully evaluated when the ::type of the outer lazy::multiplies is accessed. That way, factorial never gets instantiated with anything that isn't an Integral Constant. This is much more The Meta Way: types, not thunks. -- Eric Niebler Boost.org http://www.boost.org