boost/leaf/to_variant.hpp

0001 #ifndef BOOST_LEAF_TO_VARIANT_HPP_INCLUDED
0002 #define BOOST_LEAF_TO_VARIANT_HPP_INCLUDED
0003
0004 // Copyright 2018-2023 Emil Dotchevski and Reverge Studios, Inc.
0005
0006 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0007 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0008
0009 #if __cplusplus >= 201703L
0010
0011 #include <boost/leaf/config.hpp>
0012 #include <boost/leaf/handle_errors.hpp>
0013 #include <boost/leaf/result.hpp>
0014 #include <variant>
0015 #include <optional>
0016 #include <tuple>
0017
0018 namespace boost { namespace leaf {
0019
0020 template <class... E, class TryBlock>
0021 std::variant<typename std::decay<decltype(std::declval<TryBlock>()().value())>::type,std::tuple<std::optional<E>...>>
0022 to_variant( TryBlock && try_block )
0023 {
0024     static_assert(is_result_type<decltype(std::declval<TryBlock>()())>::value, "The return type of the try_block passed to a to_variant function must be registered with leaf::is_result_type");
0025     using T = typename std::decay<decltype(std::declval<TryBlock>()().value())>::type;
0026     using error_tuple_type = std::tuple<std::optional<E>...>;
0027     using variant_type = std::variant<T, error_tuple_type>;
0028     return try_handle_all(
0029         [&]() -> result<variant_type>
0030         {
0031             if( auto r = std::forward<TryBlock>(try_block)() )
0032                 return *std::move(r);
0033             else
0034                 return r.error();
0035         },
0036         []( E const * ... e ) -> variant_type
0037         {
0038             return error_tuple_type { e ? std::optional<E>(*e) : std::optional<E>{}... };
0039         },
0040         []() -> variant_type
0041         {
0042             return error_tuple_type { };
0043         } );
0044 }
0045
0046 } }
0047
0048 #endif
0049
0050 #endif