ladybird/AK/Optional.h
Ali Mohammad Pur 221ecf17d3 AK: Allow Optional<T&> to exist
This implements Optional<T&> as a T*, whose presence has been missing
since the early days of Optional.
As a lot of find_foo() APIs return an Optional<T> which imposes a
pointless copy on the underlying value, and can sometimes be very
misleading, with this change, those APIs can return Optional<T&>.
2022-04-04 12:48:31 +02:00

368 lines
9.9 KiB
C++

/*
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021, Daniel Bertalan <dani@danielbertalan.dev>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Assertions.h>
#include <AK/StdLibExtras.h>
#include <AK/Types.h>
#include <AK/kmalloc.h>
namespace AK {
// NOTE: If you're here because of an internal compiler error in GCC 10.3.0+,
// it's because of the following bug:
//
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96745
//
// Make sure you didn't accidentally make your destructor private before
// you start bug hunting. :^)
template<typename>
class Optional;
template<typename T>
requires(!IsLvalueReference<T>) class [[nodiscard]] Optional<T> {
template<typename U>
friend class Optional;
static_assert(!IsLvalueReference<T> && !IsRvalueReference<T>);
public:
using ValueType = T;
ALWAYS_INLINE Optional() = default;
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
Optional(Optional const& other) requires(!IsCopyConstructible<T>) = delete;
Optional(Optional const& other) = default;
Optional(Optional&& other) requires(!IsMoveConstructible<T>) = delete;
Optional& operator=(Optional const&) requires(!IsCopyConstructible<T> || !IsDestructible<T>) = delete;
Optional& operator=(Optional const&) = default;
Optional& operator=(Optional&& other) requires(!IsMoveConstructible<T> || !IsDestructible<T>) = delete;
~Optional() requires(!IsDestructible<T>) = delete;
~Optional() = default;
#endif
ALWAYS_INLINE Optional(Optional const& other)
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!IsTriviallyCopyConstructible<T>)
#endif
: m_has_value(other.m_has_value)
{
if (other.has_value())
new (&m_storage) T(other.value());
}
ALWAYS_INLINE Optional(Optional&& other)
: m_has_value(other.m_has_value)
{
if (other.has_value())
new (&m_storage) T(other.release_value());
}
template<typename U>
requires(IsConstructible<T, U const&> && !IsSpecializationOf<T, Optional> && !IsSpecializationOf<U, Optional>) ALWAYS_INLINE explicit Optional(Optional<U> const& other)
: m_has_value(other.m_has_value)
{
if (other.has_value())
new (&m_storage) T(other.value());
}
template<typename U>
requires(IsConstructible<T, U&&> && !IsSpecializationOf<T, Optional> && !IsSpecializationOf<U, Optional>) ALWAYS_INLINE explicit Optional(Optional<U>&& other)
: m_has_value(other.m_has_value)
{
if (other.has_value())
new (&m_storage) T(other.release_value());
}
template<typename U = T>
ALWAYS_INLINE explicit(!IsConvertible<U&&, T>) Optional(U&& value) requires(!IsSame<RemoveCVReference<U>, Optional<T>> && IsConstructible<T, U&&>)
: m_has_value(true)
{
new (&m_storage) T(forward<U>(value));
}
ALWAYS_INLINE Optional& operator=(Optional const& other)
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!IsTriviallyCopyConstructible<T> || !IsTriviallyDestructible<T>)
#endif
{
if (this != &other) {
clear();
m_has_value = other.m_has_value;
if (other.has_value()) {
new (&m_storage) T(other.value());
}
}
return *this;
}
ALWAYS_INLINE Optional& operator=(Optional&& other)
{
if (this != &other) {
clear();
m_has_value = other.m_has_value;
if (other.has_value()) {
new (&m_storage) T(other.release_value());
}
}
return *this;
}
template<typename O>
ALWAYS_INLINE bool operator==(Optional<O> const& other) const
{
return has_value() == other.has_value() && (!has_value() || value() == other.value());
}
template<typename O>
ALWAYS_INLINE bool operator==(O const& other) const
{
return has_value() && value() == other;
}
ALWAYS_INLINE ~Optional()
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!IsTriviallyDestructible<T>)
#endif
{
clear();
}
ALWAYS_INLINE void clear()
{
if (m_has_value) {
value().~T();
m_has_value = false;
}
}
template<typename... Parameters>
ALWAYS_INLINE void emplace(Parameters&&... parameters)
{
clear();
m_has_value = true;
new (&m_storage) T(forward<Parameters>(parameters)...);
}
[[nodiscard]] ALWAYS_INLINE bool has_value() const { return m_has_value; }
[[nodiscard]] ALWAYS_INLINE T& value() &
{
VERIFY(m_has_value);
return *__builtin_launder(reinterpret_cast<T*>(&m_storage));
}
[[nodiscard]] ALWAYS_INLINE T const& value() const&
{
VERIFY(m_has_value);
return *__builtin_launder(reinterpret_cast<T const*>(&m_storage));
}
[[nodiscard]] ALWAYS_INLINE T value() &&
{
return release_value();
}
[[nodiscard]] ALWAYS_INLINE T release_value()
{
VERIFY(m_has_value);
T released_value = move(value());
value().~T();
m_has_value = false;
return released_value;
}
[[nodiscard]] ALWAYS_INLINE T value_or(T const& fallback) const&
{
if (m_has_value)
return value();
return fallback;
}
[[nodiscard]] ALWAYS_INLINE T value_or(T&& fallback) &&
{
if (m_has_value)
return move(value());
return move(fallback);
}
ALWAYS_INLINE T const& operator*() const { return value(); }
ALWAYS_INLINE T& operator*() { return value(); }
ALWAYS_INLINE T const* operator->() const { return &value(); }
ALWAYS_INLINE T* operator->() { return &value(); }
private:
alignas(T) u8 m_storage[sizeof(T)];
bool m_has_value { false };
};
template<typename T>
requires(IsLvalueReference<T>) class [[nodiscard]] Optional<T> {
template<typename>
friend class Optional;
template<typename U>
constexpr static bool CanBePlacedInOptional = IsSame<RemoveReference<T>, RemoveReference<AddConstToReferencedType<U>>> && (IsBaseOf<RemoveCVReference<T>, RemoveCVReference<U>> || IsSame<RemoveCVReference<T>, RemoveCVReference<U>>);
public:
using ValueType = T;
ALWAYS_INLINE Optional() = default;
template<typename U = T>
ALWAYS_INLINE Optional(U& value) requires(CanBePlacedInOptional<U&>)
: m_pointer(&value)
{
}
ALWAYS_INLINE Optional(RemoveReference<T>& value)
: m_pointer(&value)
{
}
ALWAYS_INLINE Optional(Optional const& other)
: m_pointer(other.m_pointer)
{
}
ALWAYS_INLINE Optional(Optional&& other)
: m_pointer(other.m_pointer)
{
other.m_pointer = nullptr;
}
template<typename U>
ALWAYS_INLINE Optional(Optional<U> const& other) requires(CanBePlacedInOptional<U>)
: m_pointer(other.m_pointer)
{
}
template<typename U>
ALWAYS_INLINE Optional(Optional<U>&& other) requires(CanBePlacedInOptional<U>)
: m_pointer(other.m_pointer)
{
other.m_pointer = nullptr;
}
ALWAYS_INLINE Optional& operator=(Optional const& other)
{
m_pointer = other.m_pointer;
return *this;
}
ALWAYS_INLINE Optional& operator=(Optional&& other)
{
m_pointer = other.m_pointer;
other.m_pointer = nullptr;
return *this;
}
template<typename U>
ALWAYS_INLINE Optional& operator=(Optional<U> const& other) requires(CanBePlacedInOptional<U>)
{
m_pointer = other.m_pointer;
return *this;
}
template<typename U>
ALWAYS_INLINE Optional& operator=(Optional<U>&& other) requires(CanBePlacedInOptional<U>)
{
m_pointer = other.m_pointer;
other.m_pointer = nullptr;
return *this;
}
// Note: Disallows assignment from a temporary as this does not do any lifetime extension.
template<typename U>
ALWAYS_INLINE Optional& operator=(U&& value) requires(CanBePlacedInOptional<U>&& IsLvalueReference<U>)
{
m_pointer = &value;
return *this;
}
ALWAYS_INLINE void clear()
{
m_pointer = nullptr;
}
[[nodiscard]] ALWAYS_INLINE bool has_value() const { return m_pointer != nullptr; }
[[nodiscard]] ALWAYS_INLINE T value()
{
VERIFY(m_pointer);
return *m_pointer;
}
[[nodiscard]] ALWAYS_INLINE AddConstToReferencedType<T> value() const
{
VERIFY(m_pointer);
return *m_pointer;
}
template<typename U>
requires(IsBaseOf<RemoveCVReference<T>, U>) [[nodiscard]] ALWAYS_INLINE AddConstToReferencedType<T> value_or(U& fallback) const
{
if (m_pointer)
return value();
return fallback;
}
// Note that this ends up copying the value.
[[nodiscard]] ALWAYS_INLINE RemoveCVReference<T> value_or(RemoveCVReference<T> fallback) const
{
if (m_pointer)
return value();
return fallback;
}
[[nodiscard]] ALWAYS_INLINE T release_value()
{
return *exchange(m_pointer, nullptr);
}
template<typename U>
ALWAYS_INLINE bool operator==(Optional<U> const& other) const
{
return has_value() == other.has_value() && (!has_value() || value() == other.value());
}
template<typename U>
ALWAYS_INLINE bool operator==(U const& other) const
{
return has_value() && value() == other;
}
ALWAYS_INLINE AddConstToReferencedType<T> operator*() const { return value(); }
ALWAYS_INLINE T operator*() { return value(); }
ALWAYS_INLINE RawPtr<AddConst<RemoveReference<T>>> operator->() const { return &value(); }
ALWAYS_INLINE RawPtr<RemoveReference<T>> operator->() { return &value(); }
// Conversion operators from Optional<T&> -> Optional<T>
ALWAYS_INLINE operator Optional<RemoveCVReference<T>>() const
{
if (has_value())
return Optional<RemoveCVReference<T>>(value());
return {};
}
private:
RemoveReference<T>* m_pointer { nullptr };
};
}
using AK::Optional;