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Correctly direct-non-list-initialize #103

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Merged
saki7 merged 1 commit into from
Oct 2, 2026
Merged

Correctly direct-non-list-initialize #103

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50 changes: 38 additions & 12 deletions include/iris/rvariant/rvariant.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -472,15 +472,27 @@ IRIS_RVARIANT_ALWAYS_THROWING_UNREACHABLE_BEGIN
(sizeof(T) <= detail::never_valueless_trivial_size_limit && std::is_trivially_move_assignable_v<T>) ||
is_recursive_wrapper_v<T>
) {
T tmp{std::forward<Args>(args)...}; // may throw
static_assert(noexcept(t_old_i = std::move(tmp)));
t_old_i = std::move(tmp);
static_assert(noexcept(t_old_i = std::declval<T&&>()));
if constexpr (sizeof...(Args) == 0) {
T tmp = T(); // may throw
t_old_i = std::move(tmp);
} else {
T tmp(std::forward<Args>(args)...); // may throw
t_old_i = std::move(tmp);
}

} else if constexpr (
sizeof(T) <= detail::never_valueless_trivial_size_limit && std::is_trivially_copy_assignable_v<T>
) { // strange type...
T const tmp{std::forward<Args>(args)...}; // may throw
static_assert(noexcept(t_old_i = tmp));
t_old_i = tmp;
static_assert(noexcept(t_old_i = std::declval<T const&>()));
if constexpr (sizeof...(Args) == 0) {
T const tmp = T(); // may throw
t_old_i = tmp;
} else {
T const tmp(std::forward<Args>(args)...); // may throw
t_old_i = tmp;
}

} else {
static_assert(!never_valueless);
t_old_i.~T_old_i();
Expand All @@ -495,19 +507,33 @@ IRIS_RVARIANT_ALWAYS_THROWING_UNREACHABLE_BEGIN
(sizeof(T) <= detail::never_valueless_trivial_size_limit && std::is_trivially_move_constructible_v<T>) ||
is_recursive_wrapper_v<T>
) {
T tmp{std::forward<Args>(args)...}; // may throw
t_old_i.~T_old_i();
static_assert(std::is_nothrow_constructible_v<storage_type, std::in_place_index_t<I>, T&&>);
std::construct_at(&this->storage_, std::in_place_index<I>, std::move(tmp)); // never throws
if constexpr (sizeof...(Args) == 0) {
T tmp = T(); // may throw
t_old_i.~T_old_i();
std::construct_at(&this->storage_, std::in_place_index<I>, std::move(tmp)); // never throws
} else {
T tmp(std::forward<Args>(args)...); // may throw
t_old_i.~T_old_i();
std::construct_at(&this->storage_, std::in_place_index<I>, std::move(tmp)); // never throws
}
this->index_ = I;

} else if constexpr (
sizeof(T) <= detail::never_valueless_trivial_size_limit && std::is_trivially_copy_constructible_v<T>
) { // strange type...
T const tmp{std::forward<Args>(args)...}; // may throw
t_old_i.~T_old_i();
static_assert(std::is_nothrow_constructible_v<storage_type, std::in_place_index_t<I>, T const&>);
std::construct_at(&this->storage_, std::in_place_index<I>, tmp); // never throws
if constexpr (sizeof...(Args) == 0) {
T const tmp = T(); // may throw
t_old_i.~T_old_i();
std::construct_at(&this->storage_, std::in_place_index<I>, tmp); // never throws
} else {
T const tmp(std::forward<Args>(args)...); // may throw
t_old_i.~T_old_i();
std::construct_at(&this->storage_, std::in_place_index<I>, tmp); // never throws
}
this->index_ = I;

} else {
static_assert(!never_valueless);
t_old_i.~T_old_i();
Expand Down
84 changes: 80 additions & 4 deletions test/rvariant/rvariant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
#include <bit>
#include <concepts>
#include <exception>
#include <initializer_list>
#include <memory>
#include <type_traits>
#include <utility>
Expand Down Expand Up @@ -1195,11 +1196,11 @@ TEST_CASE("emplace")
using V = iris::rvariant<int, S>;
{
V v(std::in_place_type<int>);
v.emplace<S>(); // type-changing & no args; test T{}
v.emplace<S>(); // type-changing & no args; test T()
}
{
V v(std::in_place_type<S>);
v.emplace<S>(); // non-type-changing & no args; test T{}
v.emplace<S>(); // non-type-changing & no args; test T()
}
}
{
Expand All @@ -1214,15 +1215,90 @@ TEST_CASE("emplace")
using V = iris::rvariant<int, StrangeS>;
{
V v(std::in_place_type<int>);
v.emplace<StrangeS>(); // type-changing & no args; test T{}
v.emplace<StrangeS>(); // type-changing & no args; test T()
}
{
V v(std::in_place_type<StrangeS>);
v.emplace<StrangeS>(); // non-type-changing & no args; test T{}
v.emplace<StrangeS>(); // non-type-changing & no args; test T()
}
}
// NOLINTEND(modernize-use-equals-default)
}
{
// NOLINTBEGIN(modernize-use-equals-default)
// The contained value is direct-non-list-initialized ([variant.mod]): an initializer_list
// constructor is not preferred, and a narrowing into the parameter of a constructor is not
// ill-formed. `S(int)` is not `noexcept` so that the never-valueless paths are taken.
{
struct S
{
S(int value) noexcept(false) : value(value) {} // potentially-throwing
S(std::initializer_list<int>) noexcept(false) : from_list(true) {} // potentially-throwing
int value = 0;
bool from_list = false;
};
using V = iris::rvariant<int, S>;
long long wide = 42;

V v(std::in_place_type<int>);
v.emplace<S>(1); // type-changing; test T(args...)
CHECK(!iris::get<S>(v).from_list);
CHECK(iris::get<S>(v).value == 1);
v.emplace<S>(2); // non-type-changing; test T(args...)
CHECK(!iris::get<S>(v).from_list);
CHECK(iris::get<S>(v).value == 2);

V w(std::in_place_type<int>);
#ifdef _MSC_VER
# pragma warning(push)
# pragma warning(disable: 4244)
#endif
w.emplace<S>(wide); // type-changing; narrowing into `S(int)`
#ifdef _MSC_VER
# pragma warning(pop)
#endif
CHECK(iris::get<S>(w).value == 42);
w.emplace<S>(wide); // non-type-changing; narrowing into `S(int)`
CHECK(iris::get<S>(w).value == 42);
}
{
struct StrangeS
{
StrangeS(int value) noexcept(false) : value(value) {} // potentially-throwing
StrangeS(std::initializer_list<int>) noexcept(false) : from_list(true) {} // potentially-throwing
StrangeS(StrangeS&&) noexcept {} // not trivial
StrangeS(StrangeS const&) = default; // trivial
StrangeS& operator=(StrangeS&&) noexcept { return *this; } // not trivial
StrangeS& operator=(StrangeS const&) = default; // trivial
int value = 0;
bool from_list = false;
};
using V = iris::rvariant<int, StrangeS>;
long long wide = 42;

V v(std::in_place_type<int>);
v.emplace<StrangeS>(1); // type-changing; test T(args...)
CHECK(!iris::get<StrangeS>(v).from_list);
CHECK(iris::get<StrangeS>(v).value == 1);
v.emplace<StrangeS>(2); // non-type-changing; test T(args...)
CHECK(!iris::get<StrangeS>(v).from_list);
CHECK(iris::get<StrangeS>(v).value == 2);

V w(std::in_place_type<int>);
#ifdef _MSC_VER
# pragma warning(push)
# pragma warning(disable: 4244)
#endif
w.emplace<StrangeS>(wide); // type-changing; narrowing into `StrangeS(int)`
#ifdef _MSC_VER
# pragma warning(pop)
#endif
CHECK(iris::get<StrangeS>(w).value == 42);
w.emplace<StrangeS>(wide); // non-type-changing; narrowing into `StrangeS(int)`
CHECK(iris::get<StrangeS>(w).value == 42);
}
// NOLINTEND(modernize-use-equals-default)
}

// ReSharper disable CppStaticAssertFailure

Expand Down
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