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

From: vicente.botet (vicente.botet_at_[hidden])
Date: 2008-04-28 01:20:57

Hi,

----- Original Message ----- 
From: "David Abrahams" <dave_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Monday, April 28, 2008 3:50 AM
Subject: Re: [boost] [mpl] is there a or_seq like logical metafunction?

>
> 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.
>
> -- 
> Dave Abrahams
> Boost Consulting
> http://boost-consulting.com
>
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Steven Watanabe suggested also the use of find

template <typename Seq>
struct or_seq : mpl::not_<
        boost::is_same<typename mpl::find_if<Seq, mpl::_>::type,
                                    typename mpl::end<Seq>::type>
     > {};

I don't know if people needs things logical metafunctions like or_seq,
and_seq could also be the case.

I thing that these two logical metafunctions have a place in mpl.
What do you thing Aleksey?

Best regards

_____________________
Vicente Juan Botet Escriba