Aleksey Gurtovoy wrote:
Daniel Wallin writes:
I'm sorry if I'm being thick here, but I can't grasp this. To me protect looks exactly like what is needed here. I have always thought of protect as delaying the placeholder substitution one step,
Well, again, it's not what it does. If we are to talk about introducing another primitive that would cover the OP use case, then it's another discussion (which should be taken to the developers list).
Well OK, let's do that. What are your thoughts about adding something like this? template< typename BOOST_MPL_AUX_NA_PARAM(T) > struct unlambda { template< typename X = na BOOST_MPL_PP_NESTED_DEF_PARAMS_TAIL(1, typename X, na) > struct apply { typedef T type; }; typedef unlambda type; }; ... /// special case for 'unlambda' template< typename T, typename Tag > struct lambda< mpl::unlambda<T>,Tag, int_<1> > { typedef true_ is_le; typedef mpl::bind0<mpl::unlambda<T> > result_; typedef result_ type; }; -- Daniel Wallin