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

Subject: Re: [Boost-users] [Boost.Hana] how to merge two or more maps
From: Matthijs Möhlmann (matthijs_at_[hidden])
Date: 2016-08-25 09:57:32

Thank you for your answer.

Regards, Matthijs

On 8/25/16 3:06 AM, Louis Dionne wrote:
> Hana does not provide a way to merge two maps out of the box, although that
> would be very useful. I added a feature request at [1]. For now, you can use
> `fold_left` with `insert` to insert each element of the 
>
>     #include <boost/hana.hpp>
>     #include <string>
>     namespace hana = boost::hana;
>     using namespace hana::literals;
>
>     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>)
>     );
>
>     constexpr auto result = hana::fold_left(m1, m2, hana::insert);
>     constexpr auto expected = hana::make_map(
>         hana::make_pair("key1"_s, hana::type_c<std::string>),
>         hana::make_pair("key2"_s, hana::type_c<std::string>),
>         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>)
>     );
>
>     static_assert(result == expected, "");
>
>     int main() { }
>
> Also, while posting on this list is OK, please note that the preferred way
> to
> ask Hana-related questions is on StackOverflow with the [boost-hana] tag, as
> documented at [2]. This allows everybody to benefit from questions and
> answers,
> and I am registered to the tag so there's no chance that I miss your
> question
> as on this list.
>
> Regards,
> Louis
>
> [1]: https://github.com/boostorg/hana/issues/299
> [2]: http://boostorg.github.io/hana/#tutorial-support
>
>
>
>
> --
> View this message in context: http://boost.2283326.n4.nabble.com/Boost-Hana-how-to-merge-two-or-more-maps-tp4687834p4687856.html
> Sent from the Boost - Users mailing list archive at Nabble.com.
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