Re: [boost] [mpl] is there a or_seq like logical metafunction?

From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2008-04-28 05:53:26

On Mon, Apr 28, 2008 at 3:50 AM, David Abrahams
<dave_at_[hidden]> wrote:
>
>  on Fri Mar 07 2008, Steven Watanabe <watanabesj-AT-gmail.com> wrote:
>
>  > AMDG
>  >
>  > Giovanni Piero Deretta wrote:
>  >> It seems a perfect application for fold:
>  >>
>  >> template<typename Seq>
>  >> struct or_seq
>  >>     : mpl::apply<
>  >>           mpl::fold<mpl::_1, mpl::false_,  mpl::quote2<mpl::or_> >
>  >>         , Seq
>  >>       > {};
>  >>
>  >> template<typename Seq>
>  >> struct and_seq
>  >>     : mpl::apply<
>  >>           mpl::fold<mpl::_1, mpl::true_,  mpl::quote2<mpl::and_> >
>  >>         , Seq
>  >>       > {};
>  >>
>  >
>  > Not quite, because we want it to short circuit.
>  > Not to mention that quote2 will not work on and_ and or_.
>
>  Yeah, these should be rewritten in terms of mpl::find.
>  Not sure why mpl::apply was used here either, though maybe I'm missign
>  something.
>

There is, in fact, no need to use it here. I'm just so used to write
'apply' to prevent ugly "typename ... ::type" boilerplate that
instinctively stick it in mpl expressions even when they do not add
anything.

-- 
gpd