Re: [Boost-users] mpl vector of pair access

Subject: Re: [Boost-users] mpl vector of pair access
From: Olaf Peter (ope-devel_at_[hidden])
Date: 2013-04-19 14:51:45

Am 19.04.2013 19:59, schrieb Jeffrey Lee Hellrung, Jr.:
> On Fri, Apr 19, 2013 at 10:49 AM, Olaf Peter <ope-devel_at_[hidden]
> <mailto:ope-devel_at_[hidden]>> wrote:
>
>              must be  mpl::vector<
>                       mpl::vector< ...
>
>
>         Right :)
>
>
>     Thanks, now I want to find the maximum over all, but I've got lost.
>     I got it working for
>
>     typedef mpl::vector_c<std::size_t,
>                      0, // undefined,
>                      4, // foo,
>                      7  // bar,
>      > arity_info;
>
>     struct max_arity
>              : mpl::deref<
>                      mpl::max_element<arity_info>::__type
>                >::type
>     { };
>
>     but not here with the vector<vector<>> :(
>
>
> Sorry, you might have to be more specific? I'll give it a shot though. I
> would think some combination of mpl::max_element (as you have above)
> with mpl::transform (which transforms your vector<vector<...>> to a
> vector<...> of the at_c<1>'s of the inner vector<...>s) might be what
> you want, but not sure.
>
> Alternatively, you can call mpl::max_element on the original
> vector<vector<...>> nested sequence directly, using a custom comparator,
> then extract at_c<1> of the (deref'ed) result.
>
> If this is what want but you can't get either or both of the above to
> work, holler back.

You got it, thanks a lot. Here my solution:

struct arity_maximum // find the max value over all arities
        : mpl::deref<
                mpl::max_element<
                        mpl::transform<
                                  arity_info, mpl::at<mpl::_1, mpl::size_t<1> >
			>::type
		>::type
	  >::type
{ };