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- // Copyright Louis Dionne 2013-2017
- // Distributed under the Boost Software License, Version 1.0.
- // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
- #include <boost/hana/adjust_if.hpp>
- #include <boost/hana/at_key.hpp>
- #include <boost/hana/core/is_a.hpp>
- #include <boost/hana/core/to.hpp>
- #include <boost/hana/filter.hpp>
- #include <boost/hana/functional/compose.hpp>
- #include <boost/hana/functional/partial.hpp>
- #include <boost/hana/map.hpp>
- #include <boost/hana/not.hpp>
- #include <boost/hana/pair.hpp>
- #include <boost/hana/prepend.hpp>
- #include <boost/hana/string.hpp>
- #include <boost/hana/sum.hpp>
- #include <boost/hana/tuple.hpp>
- #include <boost/hana/type.hpp>
- #include <boost/hana/unpack.hpp>
- #include <cstdio>
- namespace hana = boost::hana;
- constexpr auto formats = hana::make_map(
- hana::make_pair(hana::type_c<int>, hana::string_c<'%', 'd'>),
- hana::make_pair(hana::type_c<float>, hana::string_c<'%', 'f'>),
- hana::make_pair(hana::type_c<char const*>, hana::string_c<'%', 's'>)
- );
- template <typename ...Tokens>
- constexpr auto format(Tokens ...tokens_) {
- auto tokens = hana::make_tuple(tokens_...);
- // If you don't care about constexpr-ness of `format`, you can use
- // this lambda instead of `compose(partial(...), typeid_)`:
- //
- // [](auto token) {
- // return formats[typeid_(token)];
- // }
- auto format_string_tokens = hana::adjust_if(tokens,
- hana::compose(hana::not_, hana::is_a<hana::string_tag>),
- hana::compose(hana::partial(hana::at_key, formats), hana::typeid_)
- );
- auto format_string = hana::sum<hana::string_tag>(format_string_tokens);
- auto variables = hana::filter(tokens, hana::compose(hana::not_, hana::is_a<hana::string_tag>));
- return hana::prepend(variables, format_string);
- }
- int main() {
- int a = 1;
- float b = 1.3;
- char const* c = "abcdef";
- auto args = format(
- BOOST_HANA_STRING("first="), a
- , BOOST_HANA_STRING(" second="), b
- , BOOST_HANA_STRING(" third="), c
- );
- hana::unpack(args, [](auto fmt, auto ...args) {
- std::printf(hana::to<char const*>(fmt), args...);
- });
- }
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