Skip to content

Commit

Permalink
Allow constexpr optionals.
Browse files Browse the repository at this point in the history 
Extracted from microsoft#1490 as it's unclear when that change will land.
  • Loading branch information
@BillyONeal
BillyONeal committed Oct 10, 2024
1 parent 3a7bec0 commit 007ec1e
Show file tree
Hide file tree
Showing 2 changed files with 129 additions and 84 deletions.
209 changes: 125 additions & 84 deletions include/vcpkg/base/optional.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -23,205 +23,246 @@ namespace vcpkg

namespace details
{
struct EngageTag
{
};

template<class T, bool IsTrivallyDestructible = std::is_trivially_destructible_v<T>>
struct OptionalStorageDtor
{
bool m_is_present;
union
{
char m_inactive;
T m_t;
};

constexpr OptionalStorageDtor() : m_is_present(false), m_inactive() { }
template<class... Args>
constexpr OptionalStorageDtor(EngageTag,
Args&&... args) noexcept(std::is_nothrow_constructible_v<T, Args...>)
: m_is_present(true), m_t(std::forward<Args>(args)...)
{
}
};

template<class T>
struct OptionalStorageDtor<T, false>
{
bool m_is_present;
union
{
char m_inactive;
T m_t;
};

constexpr OptionalStorageDtor() : m_is_present(false), m_inactive() { }
template<class... Args>
constexpr OptionalStorageDtor(EngageTag,
Args&&... args) noexcept(std::is_nothrow_constructible_v<T, Args...>)
: m_is_present(true), m_t(std::forward<Args>(args)...)
{
}

~OptionalStorageDtor()
{
if (m_is_present)
{
m_t.~T();
}
}
};

template<class T, bool B = std::is_copy_constructible_v<T>>
struct OptionalStorage
struct OptionalStorage : OptionalStorageDtor<T>
{
constexpr OptionalStorage() noexcept : m_is_present(false), m_inactive() { }
OptionalStorage() = default;
constexpr OptionalStorage(const T& t) noexcept(std::is_nothrow_copy_constructible_v<T>)
: m_is_present(true), m_t(t)
: OptionalStorageDtor<T>(EngageTag{}, t)
{
}
constexpr OptionalStorage(T&& t) noexcept(std::is_nothrow_move_constructible_v<T>)
: m_is_present(true), m_t(std::move(t))
: OptionalStorageDtor<T>(EngageTag{}, std::move(t))
{
}
template<class U, class = std::enable_if_t<!std::is_reference_v<U>>>
explicit OptionalStorage(Optional<U>&& t) noexcept(std::is_nothrow_constructible_v<T, U>)
: m_is_present(false), m_inactive()
: OptionalStorageDtor<T>()
{
if (auto p = t.get())
{
m_is_present = true;
new (&m_t) T(std::move(*p));
this->m_is_present = true;
new (&this->m_t) T(std::move(*p));
}
}
template<class U>
explicit OptionalStorage(const Optional<U>& t) noexcept(std::is_nothrow_constructible_v<T, const U&>)
: m_is_present(false), m_inactive()
: OptionalStorageDtor<T>()
{
if (auto p = t.get())
{
m_is_present = true;
new (&m_t) T(*p);
this->m_is_present = true;
new (&this->m_t) T(*p);
}
}

~OptionalStorage()
{
if (m_is_present) m_t.~T();
}

OptionalStorage(const OptionalStorage& o) noexcept(std::is_nothrow_copy_constructible_v<T>)
: m_is_present(o.m_is_present), m_inactive()
: OptionalStorageDtor<T>()
{
if (m_is_present) new (&m_t) T(o.m_t);
if (o.m_is_present)
{
this->m_is_present = true;
new (&this->m_t) T(o.m_t);
}
}

OptionalStorage(OptionalStorage&& o) noexcept(std::is_nothrow_move_constructible_v<T>)
: m_is_present(o.m_is_present), m_inactive()
: OptionalStorageDtor<T>()
{
if (m_is_present)
if (o.m_is_present)
{
new (&m_t) T(std::move(o.m_t));
this->m_is_present = true;
new (&this->m_t) T(std::move(o.m_t));
}
}

OptionalStorage& operator=(const OptionalStorage& o) noexcept(std::is_nothrow_copy_constructible_v<T> &&
std::is_nothrow_copy_assignable_v<T>)
{
if (m_is_present && o.m_is_present)
if (this->m_is_present && o.m_is_present)
{
m_t = o.m_t;
this->m_t = o.m_t;
}
else if (!m_is_present && o.m_is_present)
else if (!this->m_is_present && o.m_is_present)
{
new (&m_t) T(o.m_t);
m_is_present = true;
new (&this->m_t) T(o.m_t);
this->m_is_present = true;
}
else if (m_is_present && !o.m_is_present)
else if (this->m_is_present && !o.m_is_present)
{
destroy();
}

return *this;
}

OptionalStorage& operator=(OptionalStorage&& o) noexcept // enforces termination
{
if (m_is_present && o.m_is_present)
if (this->m_is_present && o.m_is_present)
{
m_t = std::move(o.m_t);
this->m_t = std::move(o.m_t);
}
else if (!m_is_present && o.m_is_present)
else if (!this->m_is_present && o.m_is_present)
{
new (&m_t) T(std::move(o.m_t));
m_is_present = true;
new (&this->m_t) T(std::move(o.m_t));
this->m_is_present = true;
}
else if (m_is_present && !o.m_is_present)
else if (this->m_is_present && !o.m_is_present)
{
destroy();
}
return *this;
}

constexpr bool has_value() const noexcept { return m_is_present; }
constexpr bool has_value() const noexcept { return this->m_is_present; }

const T& value() const noexcept { return this->m_t; }
T& value() noexcept { return this->m_t; }

const T* get() const& noexcept { return m_is_present ? &m_t : nullptr; }
T* get() & noexcept { return m_is_present ? &m_t : nullptr; }
const T* get() const& noexcept { return this->m_is_present ? &this->m_t : nullptr; }
T* get() & noexcept { return this->m_is_present ? &this->m_t : nullptr; }
const T* get() const&& = delete;
T* get() && = delete;

void destroy() noexcept // enforces termination
{
m_is_present = false;
m_t.~T();
m_inactive = '\0';
this->m_is_present = false;
this->m_t.~T();
this->m_inactive = '\0';
}

template<class... Args>
T& emplace(Args&&... args) noexcept(std::is_nothrow_constructible_v<T, Args...>)
{
if (m_is_present) destroy();
new (&m_t) T(static_cast<Args&&>(args)...);
m_is_present = true;
return m_t;
if (this->m_is_present) destroy();
new (&this->m_t) T(static_cast<Args&&>(args)...);
this->m_is_present = true;
return this->m_t;
}

private:
bool m_is_present;
union
{
char m_inactive;
T m_t;
};
};

template<class T>
struct OptionalStorage<T, false>
struct OptionalStorage<T, false> : OptionalStorageDtor<T>
{
constexpr OptionalStorage() noexcept : m_is_present(false), m_inactive() { }
OptionalStorage() = default;
constexpr OptionalStorage(T&& t) noexcept(std::is_nothrow_move_constructible_v<T>)
: m_is_present(true), m_t(std::move(t))
: OptionalStorageDtor<T>(EngageTag{}, std::move(t))
{
}

~OptionalStorage()
template<class U, class = std::enable_if_t<!std::is_reference_v<U>>>
explicit OptionalStorage(Optional<U>&& t) noexcept(std::is_nothrow_constructible_v<T, U>)
: OptionalStorageDtor<T>()
{
if (m_is_present) m_t.~T();
if (auto p = t.get())
{
this->m_is_present = true;
new (&this->m_t) T(std::move(*p));
}
}

OptionalStorage(OptionalStorage&& o) noexcept(std::is_nothrow_move_constructible_v<T>)
: m_is_present(o.m_is_present), m_inactive()
: OptionalStorageDtor<T>()
{
if (m_is_present)
if (o.m_is_present)
{
new (&m_t) T(std::move(o.m_t));
this->m_is_present = true;
new (&this->m_t) T(std::move(o.m_t));
}
}

OptionalStorage& operator=(OptionalStorage&& o) noexcept // enforces termination
{
if (m_is_present && o.m_is_present)
if (this->m_is_present && o.m_is_present)
{
m_t = std::move(o.m_t);
this->m_t = std::move(o.m_t);
}
else if (!m_is_present && o.m_is_present)
else if (!this->m_is_present && o.m_is_present)
{
m_is_present = true;
new (&m_t) T(std::move(o.m_t));
this->m_is_present = true;
new (&this->m_t) T(std::move(o.m_t));
}
else if (m_is_present && !o.m_is_present)
else if (this->m_is_present && !o.m_is_present)
{
destroy();
}

return *this;
}

constexpr bool has_value() const noexcept { return m_is_present; }
constexpr bool has_value() const noexcept { return this->m_is_present; }

const T& value() const noexcept { return this->m_t; }
T& value() noexcept { return this->m_t; }

const T* get() const& noexcept { return m_is_present ? &m_t : nullptr; }
T* get() & noexcept { return m_is_present ? &m_t : nullptr; }
const T* get() const& noexcept { return this->m_is_present ? &this->m_t : nullptr; }
T* get() & noexcept { return this->m_is_present ? &this->m_t : nullptr; }
const T* get() const&& = delete;
T* get() && = delete;

template<class... Args>
T& emplace(Args&&... args) noexcept(std::is_nothrow_constructible_v<T, Args...>)
{
if (m_is_present) destroy();
new (&m_t) T(static_cast<Args&&>(args)...);
m_is_present = true;
return m_t;
if (this->m_is_present) destroy();
new (&this->m_t) T(static_cast<Args&&>(args)...);
this->m_is_present = true;
return this->m_t;
}

void destroy() noexcept
{
m_is_present = false;
m_t.~T();
m_inactive = '\0';
this->m_is_present = false;
this->m_t.~T();
this->m_inactive = '\0';
}

private:
bool m_is_present;
union
{
char m_inactive;
T m_t;
};
};

template<class T, bool B>
Expand Down
4 changes: 4 additions & 0 deletions src/vcpkg-test/optional.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,7 @@ TEST_CASE ("value conversion", "[optional]")

Optional<long> j = 1;
Optional<int> i = j;
(void)i;
Optional<const char*> cstr = "hello, world!";
Optional<std::string> cppstr = cstr;

Expand All @@ -89,9 +90,12 @@ TEST_CASE ("optional.map", "[optional]")
const Optional<std::unique_ptr<int>> move_only;

Optional<int*> m = move_only.map([](auto&& p) { return p.get(); });
(void)m;
Optional<Optional<int*>> n =
move_only.map([](auto&& p) -> Optional<int*> { return p ? Optional<int*>{p.get()} : nullopt; });
(void)n;
Optional<NullOpt> o = move_only.map([](auto&&) { return nullopt; });
(void)o;

Optional<int> five = 5;

Expand Down

0 comments on commit 007ec1e

Please sign in to comment.