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

Subject: Re: [Boost-users] mpl::for_each state
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-03-31 19:48:31

AMDG

Skelly, Luke wrote:
> Please ignore my last message.  I somehow accidentally sent it while still editing!
>
> I am trying to create a std::map from an mpl::map.  I've been trying to figure out how to use mpl::for_each to accomplish this.  The problem I have is that the runtime function is passed to for_each by value and returns void.  All the examples I've seen for mpl::for_each involve printing and not creating any new objects.  Here is the attempt I've made:
>
> <snip>
>   
> The problem is in the call to mpl::for_each in the MapMaker constructor.  The std::map is created, but never returned.  I've considered making func_map static, but that complicates things quite a bit, especially since MapMaker it is a class template.
>   

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;
}

In Christ,
Steven Watanabe