[Boost-users] [Boost.Hana] how to merge two or more maps

Subject: [Boost-users] [Boost.Hana] how to merge two or more maps
From: Matthijs Möhlmann (matthijs_at_[hidden])
Date: 2016-08-24 06:02:17

Hi,

I am looking into the documentation of hana to merge two or more maps, say:

#include <boost/hana.hpp>

namespace hana = boost::hana;

int main(int argc, char **argv) {

    constexpr auto m1 = hana::make_map(
            hana::make_pair("key1"_s, hana::type_c<std::string>),
            hana::make_pair("key2"_s, hana::type_c<std::string>)
        );

    constexpr auto m2 = hana::make_map(
            hana::make_pair("key3"_s, hana::type_c<std::string>),
            hana::make_pair("key4"_s, hana::type_c<std::string>),
            hana::make_pair("key5"_s, hana::type_c<std::string>)
        );

    // Merge two or more maps?
    constexpr auto result = m1 + m2;

    return 0;
}

I'm not sure how to do this, probably taking the first map and for every
pair in the subsequent map return an insert? In pseudo code:

constexpr result = hana::insert(hana::insert(m1, pair1), pair2);

Can someone give me some pointers in the right direction?

Regards, Matthijs