Re: [Boost-users] [mpl] find_all type vectors in a type matrix that match a predicate.

From: David Abrahams (dave_at_[hidden])
Date: 2007-04-01 15:04:17

on Sun Apr 01 2007, "Christian Henning" <chhenning-AT-gmail.com> wrote:

> Hi there,
>
> is it possible to find all type vectors in a type matrix ( 2D type
> vector ) that match a predicate? In the end I would like to have them
> in another type matrix.

How about using filter_view?

> Can somebody point out how I would put together such a metafunction?
> I'm not sure if the mpl lib supports my feature request.
>
> Consider the following code:
>
> #include "boost/mpl/vector.hpp"
> #include <boost/mpl/find_if.hpp>
> #include <boost/mpl/at.hpp>
>
> using namespace std;
> using namespace boost;
>
> namespace fields
> {
>   struct id {};
>   struct name {};
>   struct address {};
>   struct birthday {};
> }
>
> namespace tags
> {
>   struct primary {};
>   struct foreign {};
>   struct no_key {};
> }
>
> typedef mpl::vector<fields::id      , tags::primary> id_field_t;
> typedef mpl::vector<fields::name    , tags::foreign> name_field_t;
> typedef mpl::vector<fields::address , tags::foreign> address_field_t;
> typedef mpl::vector<fields::birthday, tags::no_key> birthday_field_t;
>
>
>
> typedef mpl::vector< id_field_t
>                    , name_field_t
>                    , address_field_t
>                    , birthday_field_t
>                    > table;

  // untested
  mpl::filter_view<table, mpl::is_same<mpl::back<_>, tags::foreign> >

You can copy the filter_view into a vector if you want to, but you're
probably better off just using it as though it were a vector.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com
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