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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
Notes: sideshowbarker 2024-07-18 10:31:10 +09:00
3 changed files with 70 additions and 37 deletions
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32
AK/Variant.h
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@ -210,7 +210,27 @@ public:
template<typename... NewTs>
friend struct Variant;
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
Variant(const Variant&) requires(!(IsCopyConstructible<Ts> && ...)) = delete;
Variant(const Variant&) = default;
Variant(Variant&&) requires(!(IsMoveConstructible<Ts> && ...)) = delete;
Variant(Variant&&) = default;
~Variant() requires(!(IsDestructible<Ts> && ...)) = delete;
~Variant() = default;
Variant& operator=(const Variant&) requires(!(IsCopyConstructible<Ts> && ...) || !(IsDestructible<Ts> && ...)) = delete;
Variant& operator=(const Variant&) = default;
Variant& operator=(Variant&&) requires(!(IsMoveConstructible<Ts> && ...) || !(IsDestructible<Ts> && ...)) = delete;
Variant& operator=(Variant&&) = default;
#endif
ALWAYS_INLINE Variant(const Variant& old)
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!(IsTriviallyCopyConstructible<Ts> && ...))
#endif
: Detail::MergeAndDeduplicatePacks<Detail::VariantConstructors<Ts, Variant<Ts...>>...>()
, m_data {}
, m_index(old.m_index)
@ -223,6 +243,9 @@ public:
// and if a variant with a nontrivial move ctor is moved from, it may or may not be valid
// but it will still contain the "moved-from" state of the object it previously contained.
ALWAYS_INLINE Variant(Variant&& old)
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!(IsTriviallyMoveConstructible<Ts> && ...))
#endif
: Detail::MergeAndDeduplicatePacks<Detail::VariantConstructors<Ts, Variant<Ts...>>...>()
, m_data {}
, m_index(old.m_index)
@ -231,11 +254,17 @@ public:
}
ALWAYS_INLINE ~Variant()
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!(IsTriviallyDestructible<Ts> && ...))
#endif
{
Helper::delete_(m_index, m_data);
}
ALWAYS_INLINE Variant& operator=(const Variant& other)
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!(IsTriviallyCopyConstructible<Ts> && ...) || !(IsTriviallyDestructible<Ts> && ...))
#endif
{
m_index = other.m_index;
Helper::copy_(other.m_index, other.m_data, m_data);
@ -243,6 +272,9 @@ public:
}
ALWAYS_INLINE Variant& operator=(Variant&& other)
#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
requires(!(IsTriviallyMoveConstructible<Ts> && ...) || !(IsTriviallyDestructible<Ts> && ...))
#endif
{
m_index = other.m_index;
Helper::move_(other.m_index, other.m_data, m_data);