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Add proper type deduction to visit_by_index

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This commit is contained in:
Peter Dimov
2021-09-15 01:30:09 +03:00
parent ed4bebff3d
commit 8fd9f830a9
2 changed files with 86 additions and 10 deletions
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18
include/boost/variant2/variant.hpp
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@ -2213,27 +2213,27 @@ void swap( variant<T...> & v, variant<T...> & w )
namespace detail
{
template<class V, class... F> struct visit_by_index_L
template<class R, class V, class... F> using Vret2 = mp11::mp_eval_if_not< std::is_same<R, deduced>, R, front_if_same, mp11::mp_transform<mp11::mp_invoke_q, mp11::mp_list<Qret<F>...>, apply_cv_ref<V>> >;
template<class R, class V, class... F> struct visit_by_index_L
{
V&& v;
std::tuple<F&&...> tp;
template<class I> void operator()( I ) const
template<class I> constexpr detail::Vret2<R, V, F...> operator()( I ) const
{
std::get<I::value>( std::move(tp) )( unsafe_get<I::value>( std::forward<V>(v) ) );
return std::get<I::value>( std::move(tp) )( unsafe_get<I::value>( std::forward<V>(v) ) );
}
};
} // namespace detail
template<class V, class... F> void visit_by_index( V&& v, F&&... f )
template<class R = detail::deduced, class V, class... F> constexpr auto visit_by_index( V&& v, F&&... f ) -> detail::Vret2<R, V, F...>
{
constexpr auto N = variant_size<V>::value;
static_assert( variant_size<V>::value == sizeof...(F), "Incorrect number of function objects" );
static_assert( N == sizeof...(F), "Incorrect number of function objects" );
mp11::mp_with_index<N>( v.index(),
detail::visit_by_index_L<V, F...>{ std::forward<V>(v), std::tuple<F&&...>( std::forward<F>(f)... ) } );
return mp11::mp_with_index<variant_size<V>::value>( v.index(),
detail::visit_by_index_L<R, V, F...>{ std::forward<V>(v), std::tuple<F&&...>( std::forward<F>(f)... ) } );
}
// hashing support