Re: [Boost-users] mpl::for_each state

Subject: Re: [Boost-users] mpl::for_each state
From: Skelly, Luke (skelly_at_[hidden])
Date: 2009-04-01 10:59:34

> Have MapMaker store a reference to map.  (Warning untested code)
> 
> typedef std::map<std::size_t, std::size_t> map_type;
> 
> struct MapMaker {
>     map_type& m;
>     template<class T>
>     void operator()(T) const {
>         func_map[U::first::value]=U::second::value;
>     }
> };
> 
> template<class MplMap>
> map_type makeMap() {
>     map_type result;
>     MapMaker f = { result };
>     boost::mpl::for_each<MplMap>(f);
>     return result;
> }

Yes, since I wasn't able to send a reference directly, you're suggesting including a reference within the object being passed to mpl::for_each.  This is a nice straightforward solution and in some ways cleaner.  

I was looking for a way of sending the reference directly.  I think I've found it by using boost::ref.

typedef std::map<std::size_t, std::size_t> map_type;

struct MapMaker {
    map_type m;
    template<class T>
    void operator()(T) const {
        m[U::first::value]=U::second::value;
    }
};

template<class MplMap>
map_type makeMap() {
    MapMaker f;
    boost::mpl::for_each<MplMap>(boost::ref(f));
    return f.m;
}

Luke Skelly