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AK: Use conditionally trivial special member functions

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This commit makes use of the conditionally trivial special member
functions introduced in C++20. Basically, `Optional` and `Variant`
inherits whether its wrapped type is trivially copy constructible,
trivially copy assignable or trivially destructible. This lets the
compiler optimize optimize a large number of their use cases.

The constraints have been applied to `Optional`'s converting
constructors too in order to make the API more explicit.

This feature is not supported by Clang yet, so we use conditional
compilation so that Lagom can be built on macOS. Once Clang has P0848R3
support, these can be removed.
This commit is contained in:
Daniel Bertalan 2021-07-02 17:42:50 +02:00 • committed by Ali Mohammad Pur
parent 6c0b9919ce
commit 515e2d9734
3 changed files with 70 additions and 37 deletions
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71
AK/Optional.h
View file

@ -1,5 +1,6 @@
/*
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021, Daniel Bertalan <dani@danielbertalan.dev>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -20,23 +21,30 @@ public:
ALWAYS_INLINE Optional() = default;
ALWAYS_INLINE Optional(const T& value)
: m_has_value(true)
{
new (&m_storage) T(value);
}
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
Optional(const Optional& other) requires(!IsCopyConstructible<T>) = delete;
Optional(const Optional& other) = default;
template<typename U>
ALWAYS_INLINE Optional(const U& value)
: m_has_value(true)
{
new (&m_storage) T(value);
}
Optional(Optional&& other) requires(!IsMoveConstructible<T>) = delete;
ALWAYS_INLINE Optional(T&& value)
: m_has_value(true)
Optional& operator=(const Optional&) requires(!IsCopyConstructible<T> || !IsDestructible<T>) = delete;
Optional& operator=(const Optional&) = default;
Optional& operator=(Optional&& other) requires(!IsMoveConstructible<T> || !IsDestructible<T>) = delete;
~Optional() requires(!IsDestructible<T>) = delete;
~Optional() = default;
#endif
ALWAYS_INLINE Optional(const Optional& other)
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!IsTriviallyCopyConstructible<T>)
#endif
: m_has_value(other.m_has_value)
{
new (&m_storage) T(move(value));
if (other.has_value()) {
new (&m_storage) T(other.value());
}
}
ALWAYS_INLINE Optional(Optional&& other)
@ -44,39 +52,25 @@ public:
{
if (other.has_value()) {
new (&m_storage) T(other.release_value());
other.m_has_value = false;
}
}
ALWAYS_INLINE Optional(const Optional& other)
: m_has_value(other.m_has_value)
{
if (m_has_value) {
new (&m_storage) T(other.value());
}
}
ALWAYS_INLINE Optional(Optional& other)
: m_has_value(other.m_has_value)
{
if (m_has_value) {
new (&m_storage) T(other.value());
}
}
template<typename U>
ALWAYS_INLINE Optional(U& 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(value);
new (&m_storage) T(forward<U>(value));
}
ALWAYS_INLINE Optional& operator=(const Optional& other)
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!IsTriviallyCopyConstructible<T> || !IsTriviallyDestructible<T>)
#endif
{
if (this != &other) {
clear();
m_has_value = other.m_has_value;
if (m_has_value) {
if (other.has_value()) {
new (&m_storage) T(other.value());
}
}
@ -88,8 +82,9 @@ public:
if (this != &other) {
clear();
m_has_value = other.m_has_value;
if (other.has_value())
if (other.has_value()) {
new (&m_storage) T(other.release_value());
}
}
return *this;
}
@ -107,6 +102,9 @@ public:
}
ALWAYS_INLINE ~Optional()
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!IsTriviallyDestructible<T>)
#endif
{
clear();
}
@ -167,7 +165,6 @@ private:
alignas(T) u8 m_storage[sizeof(T)];
bool m_has_value { false };
};
}
using AK::Optional;