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

Subject: Re: [boost] [mpl] is there a or_seq like logical metafunction?
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2009-02-10 13:45:24

----- Original Message ----- 
From: "Larry Evans" <cppljevans_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Sunday, February 08, 2009 2:50 PM
Subject: Re: [boost] [mpl] is there a or_seq like logical metafunction?

> 
> On 02/07/09 13:58, Larry Evans wrote:
>> On 02/07/09 13:29, vicente.botet wrote:
> [snip]
>>> After suggestion of I don't remember who, I have implemented it as
>>>
>>> /* Calculate the mlp::and_ of a sequence of nullary logical 
>>> metafunctions.*/    template <typename Seq>
>>> struct and_seq : boost::is_same<typename mpl::find_if<Seq, 
>>> mpl::not_<mpl::_> >::type,            typename mpl::end<Seq>::type> 
>>>      {};
>> [snip]
>>>
>>> If there are better ways to do that, you don't tink that this must be 
>>> encapsulated in the library? Why not add these metafunctions in 
>>> Boost.MPL?
>>>
>>> Thanks,
>> 
>> OOPS.  I misread the post.  I was just thinking of and_ and or_.
>> I missed the "sequence of nullary logical metafunctions".
>> Sorry for noise.  It just seemed so similar I neglected
>> any differences.
> 
> Aren't true_ and false_ nullary logical metafunctions.  If
> so then I think what you're requiring is someway to
> "unpack" the args from Seq<T1,T2,...Tn> into and_<T1,T2,...,Tn>
> or or_<T1,T2,...,Tn>. Could:
> 
> http://www.boost.org/doc/libs/1_37_0/libs/mpl/doc/refmanual/unpack-args.html
> 
> be used to do that?  

Oh! this is quite interesting. I will try it to see how it works. WHich implementation should perdorms better if any difference?

> If not, then it's pretty easy to do that
> with the variadic version of mpl since all Sequences are
> derived from package<T1,T2,...,Tn> so:
> 
>   template<typename... T>
>   or_seq<package<T...> >
>   : or_<T...>
>   {};
> 
> A prototype variadic version of mpl is in the boost vault.

Thanks for the pointer,

Vicente