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Compute the index type with a metafunction. Refs #50.
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@pdimov
pdimov committed Dec 21, 2024
1 parent 509ce1d commit 306a602
Showing 1 changed file with 34 additions and 5 deletions.
39 changes: 34 additions & 5 deletions include/boost/variant2/variant.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#include <iosfwd>
#include <cstdint>
#include <cerrno>
#include <limits>

//

Expand Down Expand Up @@ -845,6 +846,10 @@ template<class U, class... T> using resolve_overload_type = typename decltype( o

template<class U, class... T> using resolve_overload_index = mp11::mp_find<mp11::mp_list<T...>, resolve_overload_type<U, T...>>;

// index_type

template<bool Double, class... T> using get_index_type = unsigned;

// variant_base

template<bool is_trivially_destructible, bool is_single_buffered, class... T> struct variant_base_impl;
Expand All @@ -855,8 +860,10 @@ struct none {};
// trivially destructible, single buffered
template<class... T> struct variant_base_impl<true, true, T...>
{
using index_type = get_index_type<false, T...>;

variant_storage<none, T...> st_;
unsigned ix_;
index_type ix_;

constexpr variant_base_impl(): st_( mp11::mp_size_t<0>() ), ix_( 0 )
{
Expand All @@ -870,6 +877,8 @@ template<class... T> struct variant_base_impl<true, true, T...>
template<class I, class... A> void _replace( I, A&&... a )
{
::new( &st_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );

static_assert( I::value + 1 <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = I::value + 1;
}

Expand Down Expand Up @@ -901,6 +910,8 @@ template<class... T> struct variant_base_impl<true, true, T...>
static_assert( std::is_nothrow_constructible<U, A&&...>::value, "Logic error: U must be nothrow constructible from A&&..." );

st_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );

static_assert( J <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = J;
}

Expand All @@ -911,6 +922,8 @@ template<class... T> struct variant_base_impl<true, true, T...>
U tmp( std::forward<A>(a)... );

st_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );

static_assert( J <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = J;
}

Expand All @@ -931,8 +944,10 @@ template<class... T> struct variant_base_impl<true, true, T...>
// trivially destructible, double buffered
template<class... T> struct variant_base_impl<true, false, T...>
{
using index_type = get_index_type<true, T...>;

variant_storage<none, T...> st_[ 2 ];
unsigned ix_;
index_type ix_;

constexpr variant_base_impl(): st_{ { mp11::mp_size_t<0>() }, { mp11::mp_size_t<0>() } }, ix_( 0 )
{
Expand All @@ -946,6 +961,8 @@ template<class... T> struct variant_base_impl<true, false, T...>
template<class I, class... A> void _replace( I, A&&... a )
{
::new( &st_[ 0 ] ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );

static_assert( ( I::value + 1 ) * 2 <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = ( I::value + 1 ) * 2;
}

Expand Down Expand Up @@ -982,6 +999,7 @@ template<class... T> struct variant_base_impl<true, false, T...>

st_[ i2 ].emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );

static_assert( J * 2 + 1 <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = J * 2 + i2;
}

Expand All @@ -994,8 +1012,10 @@ template<class... T> struct variant_base_impl<true, false, T...>
// not trivially destructible, single buffered
template<class... T> struct variant_base_impl<false, true, T...>
{
using index_type = get_index_type<false, T...>;

variant_storage<none, T...> st_;
unsigned ix_;
index_type ix_;

constexpr variant_base_impl(): st_( mp11::mp_size_t<0>() ), ix_( 0 )
{
Expand All @@ -1009,6 +1029,8 @@ template<class... T> struct variant_base_impl<false, true, T...>
template<class I, class... A> void _replace( I, A&&... a )
{
::new( &st_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );

static_assert( I::value + 1 <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = I::value + 1;
}

Expand Down Expand Up @@ -1077,6 +1099,8 @@ template<class... T> struct variant_base_impl<false, true, T...>
_destroy();

st_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );

static_assert( J <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = J;
}

Expand All @@ -1089,12 +1113,14 @@ template<class... T> struct variant_base_impl<false, true, T...>
// not trivially destructible, double buffered
template<class... T> struct variant_base_impl<false, false, T...>
{
using index_type = get_index_type<true, T...>;

#if defined(__GNUC__) && __GNUC__ < 11 && !defined(__clang__) && !defined(__INTEL_COMPILER)

// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63707 :-(

variant_storage<none, T...> st1_, st2_;
unsigned ix_;
index_type ix_;

constexpr variant_base_impl(): st1_( mp11::mp_size_t<0>() ), st2_( mp11::mp_size_t<0>() ), ix_( 0 )
{
Expand All @@ -1117,7 +1143,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
#else

variant_storage<none, T...> st_[ 2 ];
unsigned ix_;
index_type ix_;

constexpr variant_base_impl(): st_{ { mp11::mp_size_t<0>() }, { mp11::mp_size_t<0>() } }, ix_( 0 )
{
Expand All @@ -1143,6 +1169,8 @@ template<class... T> struct variant_base_impl<false, false, T...>
template<class I, class... A> void _replace( I, A&&... a )
{
::new( &storage( 0 ) ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );

static_assert( ( I::value + 1 ) * 2 <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = ( I::value + 1 ) * 2;
}

Expand Down Expand Up @@ -1207,6 +1235,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
storage( i2 ).emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
_destroy();

static_assert( J * 2 + 1 <= (std::numeric_limits<index_type>::max)(), "" );
ix_ = J * 2 + i2;
}

Expand Down

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