Re: [Boost-users] Comparing two mpl::vector types

Subject: Re: [Boost-users] Comparing two mpl::vector types
From: Jeffrey Lee Hellrung, Jr. (jeffrey.hellrung_at_[hidden])
Date: 2013-02-23 02:10:04

On Fri, Feb 22, 2013 at 4:32 PM, Rodrigo Madera <rodrigo.madera_at_[hidden]>wrote:

> Hello all,
>
> Can anyone give me a hint on how to call a functor on the differences of
> two same size mpl::vector types?
>
> For example, given:
>
> typedef boost::mpl::vector<int, char, short, double> v0_type;
> typedef boost::mpl::vector<int, int, short, std::string> v1_type;
>
> We can see that the second and third elements don't match, so I wish to
> call a functor twice, with the following signature:
>
> struct SomeFunctor {
>         template <typename T, typename U>
>         void operator()(T t, U u) const {
>                 // do something nice here
>         }
> };
>
> In this example, functor would be called twice: once with [T=char, U=int]
> and another with [T=short, U=std::string], along with their values.
>

Looks like using a zip_view [1] followed by a filter_view [2] followed by a
for_each [3] will get you what you want. E.g., (untested)

typedef mpl::zip_view< mpl::vector2< v0_type, v1_type > > zip_view_type;
typedef mpl::filter_view< zip_view_type, mpl::not_< boost::is_same<
mpl::_1, mpl::_2 > > > filter_view_type;
mpl::for_each< filter_view_type >(SomeFunctor());

HTH,

- Jeff

[1]
http://www.boost.org/doc/libs/1_53_0/libs/mpl/doc/refmanual/zip-view.html
[2]
http://www.boost.org/doc/libs/1_53_0/libs/mpl/doc/refmanual/filter-view.html
[3]
http://www.boost.org/doc/libs/1_53_0/libs/mpl/doc/refmanual/for-each.html