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Support derived types in visit

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This commit is contained in:
Peter Dimov
2020-05-06 20:11:03 +03:00
parent f3b3b533aa
commit 772ef0d312
3 changed files with 84 additions and 6 deletions
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31
include/boost/variant2/variant.hpp
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@ -1768,6 +1768,25 @@ namespace detail
template<class T> using remove_cv_ref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
template<class... T> variant<T...> const & extract_variant_base_( variant<T...> const & );
#if BOOST_WORKAROUND( BOOST_MSVC, < 1930 )
template<class V> struct extract_vbase_impl
{
using type = decltype( extract_variant_base_( std::declval<V>() ) );
};
template<class V> using extract_variant_base = remove_cv_ref_t< typename extract_vbase_impl<V>::type >;
#else
template<class V> using extract_variant_base = remove_cv_ref_t< decltype( extract_variant_base_( std::declval<V>() ) ) >;
#endif
template<class V> using variant_base_size = variant_size< extract_variant_base<V> >;
template<class T, class U> struct copy_cv_ref
{
using type = T;
@ -1807,7 +1826,7 @@ template<class F> struct Qret
template<class L> using front_if_same = mp11::mp_if<mp11::mp_apply<mp11::mp_same, L>, mp11::mp_front<L>>;
template<class V> using apply_cv_ref = mp11::mp_product<copy_cv_ref_t, remove_cv_ref_t<V>, mp11::mp_list<V>>;
template<class V> using apply_cv_ref = mp11::mp_product<copy_cv_ref_t, extract_variant_base<V>, mp11::mp_list<V>>;
template<class F, class... V> using Vret = front_if_same<mp11::mp_product_q<Qret<F>, apply_cv_ref<V>...>>;
@ -1836,7 +1855,7 @@ template<class F, class V1> struct visit_L1
template<class F, class V1> constexpr auto visit( F&& f, V1&& v1 ) -> detail::Vret<F, V1>
{
return mp11::mp_with_index<variant_size<V1>>( v1.index(), detail::visit_L1<F, V1>{ std::forward<F>(f), std::forward<V1>(v1) } );
return mp11::mp_with_index<detail::variant_base_size<V1>>( v1.index(), detail::visit_L1<F, V1>{ std::forward<F>(f), std::forward<V1>(v1) } );
}
#if defined(BOOST_NO_CXX14_GENERIC_LAMBDAS) || BOOST_WORKAROUND( BOOST_MSVC, < 1920 )
@ -1878,7 +1897,7 @@ template<class F, class V1, class V2> struct visit_L2
template<class F, class V1, class V2> constexpr auto visit( F&& f, V1&& v1, V2&& v2 ) -> detail::Vret<F, V1, V2>
{
return mp11::mp_with_index<variant_size<V1>>( v1.index(), detail::visit_L2<F, V1, V2>{ std::forward<F>(f), std::forward<V1>(v1), std::forward<V2>(v2) } );
return mp11::mp_with_index<detail::variant_base_size<V1>>( v1.index(), detail::visit_L2<F, V1, V2>{ std::forward<F>(f), std::forward<V1>(v1), std::forward<V2>(v2) } );
}
namespace detail
@ -1903,7 +1922,7 @@ template<class F, class V1, class V2, class V3> struct visit_L3
template<class F, class V1, class V2, class V3> constexpr auto visit( F&& f, V1&& v1, V2&& v2, V3&& v3 ) -> detail::Vret<F, V1, V2, V3>
{
return mp11::mp_with_index<variant_size<V1>>( v1.index(), detail::visit_L3<F, V1, V2, V3>{ std::forward<F>(f), std::forward<V1>(v1), std::forward<V2>(v2), std::forward<V3>(v3) } );
return mp11::mp_with_index<detail::variant_base_size<V1>>( v1.index(), detail::visit_L3<F, V1, V2, V3>{ std::forward<F>(f), std::forward<V1>(v1), std::forward<V2>(v2), std::forward<V3>(v3) } );
}
namespace detail
@ -1929,14 +1948,14 @@ template<class F, class V1, class V2, class V3, class V4> struct visit_L4
template<class F, class V1, class V2, class V3, class V4> constexpr auto visit( F&& f, V1&& v1, V2&& v2, V3&& v3, V4&& v4 ) -> detail::Vret<F, V1, V2, V3, V4>
{
return mp11::mp_with_index<variant_size<V1>>( v1.index(), detail::visit_L4<F, V1, V2, V3, V4>{ std::forward<F>(f), std::forward<V1>(v1), std::forward<V2>(v2), std::forward<V3>(v3), std::forward<V4>(v4) } );
return mp11::mp_with_index<detail::variant_base_size<V1>>( v1.index(), detail::visit_L4<F, V1, V2, V3, V4>{ std::forward<F>(f), std::forward<V1>(v1), std::forward<V2>(v2), std::forward<V3>(v3), std::forward<V4>(v4) } );
}
#else
template<class F, class V1, class V2, class... V> constexpr auto visit( F&& f, V1&& v1, V2&& v2, V&&... v ) -> detail::Vret<F, V1, V2, V...>
{
return mp11::mp_with_index<variant_size<V1>>( v1.index(), [&]( auto I ){
return mp11::mp_with_index<detail::variant_base_size<V1>>( v1.index(), [&]( auto I ){
auto f2 = [&]( auto&&... a ){ return std::forward<F>(f)( detail::unsafe_get<I.value>( std::forward<V1>(v1) ), std::forward<decltype(a)>(a)... ); };
return visit( f2, std::forward<V2>(v2), std::forward<V>(v)... );

2
test/Jamfile
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@ -110,3 +110,5 @@ run variant_hash.cpp ;
run variant_trivial.cpp ;
run variant_special.cpp ;
run variant_visit_derived.cpp ;

57
test/variant_visit_derived.cpp Normal file
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@ -0,0 +1,57 @@
// Copyright 2017, 2020 Peter Dimov.
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt
#if defined(_MSC_VER)
# pragma warning( disable: 4244 ) // conversion from float to int, possible loss of data
#endif
#include <boost/variant2/variant.hpp>
#include <boost/core/lightweight_test.hpp>
#include <boost/config.hpp>
#include <boost/config/workaround.hpp>
#include <utility>
struct X: boost::variant2::variant<int, float>
{
#if BOOST_WORKAROUND( BOOST_MSVC, < 1930 )
template<class T> explicit X( T&& t ): variant( std::forward<T>( t ) ) {};
#else
using variant::variant;
#endif
};
template<class... T> struct Y: boost::variant2::variant<T...>
{
using boost::variant2::variant<T...>::variant;
};
int main()
{
{
X v1( 1 );
X const v2( 3.14f );
BOOST_TEST_EQ( (visit( []( int x1, float x2 ){ return (int)(x1 * 1000) + (int)(x2 * 100); }, v1, v2 )), 1314 );
visit( []( int x1, float x2 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); }, v1, v2 );
visit( []( int x1, float x2 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); }, std::move(v1), std::move(v2) );
}
{
Y<int, float> v1( 1 );
Y<int, float> const v2( 3.14f );
BOOST_TEST_EQ( (visit( []( int x1, float x2 ){ return (int)(x1 * 1000) + (int)(x2 * 100); }, v1, v2 )), 1314 );
visit( []( int x1, float x2 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); }, v1, v2 );
visit( []( int x1, float x2 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); }, std::move(v1), std::move(v2) );
}
return boost::report_errors();
}