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Merged
steve-downey merged 4 commits into from
Jan 6, 2025
Merged

When moving a 'optional<T&>', don't move the remote value #93

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3632ace
When moving a 'optional<T&>', don't move the remote value
jiixyj Dec 31, 2024
c891a22
Add separate constructors and assignment operators from 'optional<T&>'
jiixyj Jan 3, 2025
ab3eedf
Fix middle argument to 'enable_from_other' for construct/assign from …
jiixyj Jan 3, 2025
e5fab32
Merge remote-tracking branch 'origin/main' into shallow-value-categor…
jiixyj Jan 6, 2025
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80 changes: 68 additions & 12 deletions include/beman/optional26/optional.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -276,19 +276,29 @@ class optional {

template <class U>
constexpr explicit(!std::is_convertible_v<U, T>) optional(const optional<U>& rhs)
requires detail::enable_from_other<T, U, const U&> && std::is_convertible_v<const U&, T>;
requires(!std::is_reference_v<U> && detail::enable_from_other<T, U, const U&> &&
std::is_convertible_v<const U&, T>);

template <class U>
constexpr explicit(!std::is_convertible_v<U, T>) optional(const optional<U>& rhs)
requires detail::enable_from_other<T, U, const U&> && (!std::is_convertible_v<const U&, T>);
requires(!std::is_reference_v<U> && detail::enable_from_other<T, U, const U&> &&
!std::is_convertible_v<const U&, T>);

template <class U>
constexpr explicit(!std::is_convertible_v<U, T>) optional(optional<U>&& rhs)
requires detail::enable_from_other<T, U, U&&> && std::is_convertible_v<U&&, T>;
requires(!std::is_reference_v<U> && detail::enable_from_other<T, U, U &&> && std::is_convertible_v<U &&, T>);

template <class U>
constexpr explicit(!std::is_convertible_v<U, T>) optional(optional<U>&& rhs)
requires detail::enable_from_other<T, U, U&&> && (!std::is_convertible_v<U &&, T>);
requires(!std::is_reference_v<U> && detail::enable_from_other<T, U, U &&> && !std::is_convertible_v<U &&, T>);

template <class U>
constexpr explicit(!std::is_convertible_v<U&, T>) optional(const optional<U&>& rhs)
requires(detail::enable_from_other<T, U&, U&> && std::is_convertible_v<U&, T>);

template <class U>
constexpr explicit(!std::is_convertible_v<U&, T>) optional(const optional<U&>& rhs)
requires(detail::enable_from_other<T, U&, U&> && !std::is_convertible_v<U&, T>);

// \ref{optional.dtor}, destructor
constexpr ~optional()
Expand Down Expand Up @@ -325,11 +335,15 @@ class optional {

template <class U>
constexpr optional& operator=(const optional<U>& rhs)
requires detail::enable_assign_from_other<T, U, const U&>;
requires(!std::is_reference_v<U> && detail::enable_assign_from_other<T, U, const U&>);

template <class U>
constexpr optional& operator=(optional<U>&& rhs)
requires detail::enable_assign_from_other<T, U, U>;
requires(!std::is_reference_v<U> && detail::enable_assign_from_other<T, U, U>);

template <class U>
constexpr optional& operator=(const optional<U&>& rhs)
requires(detail::enable_assign_from_other<T, U&, U&>);

template <class... Args>
constexpr T& emplace(Args&&... args);
Expand Down Expand Up @@ -463,7 +477,8 @@ inline constexpr optional<T>::optional(U&& u)
template <class T>
template <class U>
inline constexpr optional<T>::optional(const optional<U>& rhs)
requires detail::enable_from_other<T, U, const U&> && std::is_convertible_v<const U&, T>
requires(!std::is_reference_v<U> && detail::enable_from_other<T, U, const U&> &&
std::is_convertible_v<const U&, T>)
{
if (rhs.has_value()) {
construct(*rhs);
Expand All @@ -473,7 +488,8 @@ inline constexpr optional<T>::optional(const optional<U>& rhs)
template <class T>
template <class U>
inline constexpr optional<T>::optional(const optional<U>& rhs)
requires detail::enable_from_other<T, U, const U&> && (!std::is_convertible_v<const U&, T>)
requires(!std::is_reference_v<U> && detail::enable_from_other<T, U, const U&> &&
!std::is_convertible_v<const U&, T>)
{
if (rhs.has_value()) {
construct(*rhs);
Expand All @@ -484,7 +500,7 @@ inline constexpr optional<T>::optional(const optional<U>& rhs)
template <class T>
template <class U>
inline constexpr optional<T>::optional(optional<U>&& rhs)
requires detail::enable_from_other<T, U, U&&> && std::is_convertible_v<U&&, T>
requires(!std::is_reference_v<U> && detail::enable_from_other<T, U, U &&> && std::is_convertible_v<U &&, T>)
{
if (rhs.has_value()) {
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@steve-downey steve-downey Jan 2, 2025

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https://eel.is/c++draft/optional#ctor-34 means this needs a paper.

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@jiixyj jiixyj Jan 2, 2025

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Yep, and there is https://eel.is/c++draft/optional#assign-25 as well.

Although in a world where only optional<T> exists I believe std::move(*rhs) and *std::move(rhs) do the same thing. So implementers could have used the as-if rule this whole time. Only for optional<T&> there might be a semantic difference. Maybe P2988 is a good vehicle for this?

construct(std::move(*rhs));
Expand All @@ -494,13 +510,33 @@ inline constexpr optional<T>::optional(optional<U>&& rhs)
template <class T>
template <class U>
inline constexpr optional<T>::optional(optional<U>&& rhs)
requires detail::enable_from_other<T, U, U&&> && (!std::is_convertible_v<U &&, T>)
requires(!std::is_reference_v<U> && detail::enable_from_other<T, U, U &&> && !std::is_convertible_v<U &&, T>)
{
if (rhs.has_value()) {
construct(std::move(*rhs));
}
}

template <class T>
template <class U>
inline constexpr optional<T>::optional(const optional<U&>& rhs)
requires(detail::enable_from_other<T, U&, U&> && std::is_convertible_v<U&, T>)
{
if (rhs.has_value()) {
construct(*rhs);
}
}

template <class T>
template <class U>
inline constexpr optional<T>::optional(const optional<U&>& rhs)
requires(detail::enable_from_other<T, U&, U&> && !std::is_convertible_v<U&, T>)
{
if (rhs.has_value()) {
construct(*rhs);
}
}

// 22.5.3.3 Destructor[optional.dtor]

template <class T>
Expand Down Expand Up @@ -571,7 +607,7 @@ inline constexpr optional<T>& optional<T>::operator=(U&& u)
template <class T>
template <class U>
inline constexpr optional<T>& optional<T>::operator=(const optional<U>& rhs)
requires detail::enable_assign_from_other<T, U, const U&>
requires(!std::is_reference_v<U> && detail::enable_assign_from_other<T, U, const U&>)
{
if (has_value()) {
if (rhs.has_value()) {
Expand All @@ -595,7 +631,7 @@ inline constexpr optional<T>& optional<T>::operator=(const optional<U>& rhs)
template <class T>
template <class U>
inline constexpr optional<T>& optional<T>::operator=(optional<U>&& rhs)
requires detail::enable_assign_from_other<T, U, U>
requires(!std::is_reference_v<U> && detail::enable_assign_from_other<T, U, U>)
{
if (has_value()) {
if (rhs.has_value()) {
Expand All @@ -612,6 +648,26 @@ inline constexpr optional<T>& optional<T>::operator=(optional<U>&& rhs)
return *this;
}

template <class T>
template <class U>
inline constexpr optional<T>& optional<T>::operator=(const optional<U&>& rhs)
requires(detail::enable_assign_from_other<T, U&, U&>)
{
if (has_value()) {
if (rhs.has_value()) {
value_ = *rhs;
} else {
hard_reset();
}
}

else if (rhs.has_value()) {
construct(*rhs);
}

return *this;
}

/// Constructs the value in-place, destroying the current one if there is
/// one.
template <class T>
Expand Down
91 changes: 91 additions & 0 deletions src/beman/optional26/tests/optional.t.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -914,3 +914,94 @@ TEST(OptionalTest, CanHoldValueOfImmovableType) {
beman::optional26::optional<immovable> o2 = beman::optional26::nullopt;
EXPECT_FALSE(o2);
}

// Moving an `optional<T&>` should not move the remote value.
TEST(OptionalTest, OptionalFromOptionalRef) {
using beman::optional26::tests::copyable_from_non_const_lvalue_only;

copyable_from_non_const_lvalue_only cm;

beman::optional26::optional<copyable_from_non_const_lvalue_only&> o1 = cm;
ASSERT_TRUE(o1);

{
beman::optional26::optional<copyable_from_non_const_lvalue_only> o2 = o1;
ASSERT_TRUE(o2);
}

beman::optional26::optional<copyable_from_non_const_lvalue_only> o2 = std::move(o1);
ASSERT_TRUE(o2);

o2 = o1;
ASSERT_TRUE(o2);

o2 = std::move(o1);
ASSERT_TRUE(o2);

o2.reset();
o2 = o1;
ASSERT_TRUE(o2);

o2.reset();
o2 = std::move(o1);
ASSERT_TRUE(o2);
}

TEST(OptionalTest, OptionalFromOptionalRefExplicit) {
using beman::optional26::tests::copyable_from_non_const_lvalue_only;
using beman::optional26::tests::explicitly_convertible_from_non_const_lvalue_only;

explicitly_convertible_from_non_const_lvalue_only ec;

beman::optional26::optional<explicitly_convertible_from_non_const_lvalue_only&> o3 = ec;

beman::optional26::optional<copyable_from_non_const_lvalue_only> o4(o3);
ASSERT_TRUE(o4);
beman::optional26::optional<copyable_from_non_const_lvalue_only> o5(std::move(o3));
ASSERT_TRUE(o5);
}

TEST(OptionalTest, OptionalFromOptionalConstRef) {
using beman::optional26::tests::copyable_from_const_lvalue_only;

copyable_from_const_lvalue_only cm;

beman::optional26::optional<const copyable_from_const_lvalue_only&> o1 = cm;
ASSERT_TRUE(o1);

{
beman::optional26::optional<copyable_from_const_lvalue_only> o2 = o1;
ASSERT_TRUE(o2);
}

beman::optional26::optional<copyable_from_const_lvalue_only> o2 = std::move(o1);
ASSERT_TRUE(o2);

o2 = o1;
ASSERT_TRUE(o2);

o2 = std::move(o1);
ASSERT_TRUE(o2);

o2.reset();
o2 = o1;
ASSERT_TRUE(o2);

o2.reset();
o2 = std::move(o1);
ASSERT_TRUE(o2);
}

TEST(OptionalTest, OptionalFromOptionalConstRefExplicit) {
using beman::optional26::tests::copyable_from_const_lvalue_only;
using beman::optional26::tests::explicitly_convertible_from_const_lvalue_only;

explicitly_convertible_from_const_lvalue_only ec;

beman::optional26::optional<const explicitly_convertible_from_const_lvalue_only&> o3 = ec;

beman::optional26::optional<copyable_from_const_lvalue_only> o4(o3);
ASSERT_TRUE(o4);
beman::optional26::optional<copyable_from_const_lvalue_only> o5(std::move(o3));
ASSERT_TRUE(o5);
}
38 changes: 38 additions & 0 deletions src/beman/optional26/tests/test_types.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,44 @@ struct immovable {
immovable& operator=(const immovable&) = delete;
};

struct copyable_from_non_const_lvalue_only {
explicit copyable_from_non_const_lvalue_only() = default;
copyable_from_non_const_lvalue_only(copyable_from_non_const_lvalue_only&) = default;
copyable_from_non_const_lvalue_only(const copyable_from_non_const_lvalue_only&) = delete;
copyable_from_non_const_lvalue_only(copyable_from_non_const_lvalue_only&&) = delete;
copyable_from_non_const_lvalue_only(const copyable_from_non_const_lvalue_only&&) = delete;
copyable_from_non_const_lvalue_only& operator=(copyable_from_non_const_lvalue_only&) = default;
copyable_from_non_const_lvalue_only& operator=(const copyable_from_non_const_lvalue_only&) = delete;
copyable_from_non_const_lvalue_only& operator=(copyable_from_non_const_lvalue_only&&) = delete;
copyable_from_non_const_lvalue_only& operator=(const copyable_from_non_const_lvalue_only&&) = delete;
};

struct explicitly_convertible_from_non_const_lvalue_only {
explicit operator copyable_from_non_const_lvalue_only() & { return copyable_from_non_const_lvalue_only{}; }
explicit operator copyable_from_non_const_lvalue_only() const& = delete;
explicit operator copyable_from_non_const_lvalue_only() && = delete;
explicit operator copyable_from_non_const_lvalue_only() const&& = delete;
};

struct copyable_from_const_lvalue_only {
explicit copyable_from_const_lvalue_only() = default;
copyable_from_const_lvalue_only(copyable_from_const_lvalue_only&) = delete;
copyable_from_const_lvalue_only(const copyable_from_const_lvalue_only&) = default;
copyable_from_const_lvalue_only(copyable_from_const_lvalue_only&&) = delete;
copyable_from_const_lvalue_only(const copyable_from_const_lvalue_only&&) = delete;
copyable_from_const_lvalue_only& operator=(copyable_from_const_lvalue_only&) = delete;
copyable_from_const_lvalue_only& operator=(const copyable_from_const_lvalue_only&) = default;
copyable_from_const_lvalue_only& operator=(copyable_from_const_lvalue_only&&) = delete;
copyable_from_const_lvalue_only& operator=(const copyable_from_const_lvalue_only&&) = delete;
};

struct explicitly_convertible_from_const_lvalue_only {
explicit operator copyable_from_const_lvalue_only() & = delete;
explicit operator copyable_from_const_lvalue_only() const& { return copyable_from_const_lvalue_only{}; }
explicit operator copyable_from_const_lvalue_only() && = delete;
explicit operator copyable_from_const_lvalue_only() const&& = delete;
};

} // namespace beman::optional26::tests

#endif // BEMAN_OPTIONAL26_TESTS_TEST_TYPES_HPP
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