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AK: Add SentinelOptional

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We specialize `Optional<T>` for value types that inherently support some
kind of "empty" value or whose value range allow for a unlikely to be
useful sentinel value that can mean "empty", instead of the boolean flag
a regular Optional<T> needs to store. Because of padding, this often
means saving 4 to 8 bytes per instance.

By extending the new `SentinelOptional<T, Traits>`, these
specializations are significantly simplified to just having to define
what the sentinel value is, and how to identify a sentinel value.
This commit is contained in:
Jelle Raaijmakers
2026-03-18 20:43:56 +01:00
committed by Jelle Raaijmakers
parent 9e245b014c
commit e123d48043
Notes: github-actions[bot] 2026-03-20 11:04:58 +00:00 
Author: https://github.com/gmta
Commit: https://github.com/LadybirdBrowser/ladybird/commit/e123d480436
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/8508
Reviewed-by: https://github.com/konradekk
13 changed files with 215 additions and 988 deletions
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100
Libraries/LibJS/Runtime/PropertyKey.h
View File

@@ -179,7 +179,7 @@ public:
private:
friend Traits<PropertyKey>;
friend class Optional<PropertyKey>;
friend struct AK::SentinelOptionalTraits<PropertyKey>;
enum class ShouldMakeEmptyOptional {
Indeed,
@@ -242,99 +242,15 @@ struct Formatter<JS::PropertyKey> : Formatter<Utf16String> {
};
template<>
class Optional<JS::PropertyKey> : public OptionalBase<JS::PropertyKey> {
template<typename U>
friend class Optional;
struct SentinelOptionalTraits<JS::PropertyKey> {
static JS::PropertyKey sentinel_value() { return JS::PropertyKey { JS::PropertyKey::ShouldMakeEmptyOptional::Indeed }; }
static bool is_sentinel(JS::PropertyKey const& value) { return value.is_empty_optional(); }
};
template<>
class Optional<JS::PropertyKey> : public SentinelOptional<JS::PropertyKey> {
public:
using ValueType = JS::PropertyKey;
Optional() = default;
template<SameAs<OptionalNone> V>
Optional(V) { }
Optional(Optional<JS::PropertyKey> const& other)
{
if (other.has_value())
m_value = other.m_value;
}
Optional(Optional&& other)
: m_value(other.m_value)
{
}
template<typename U = JS::PropertyKey>
requires(!IsSame<OptionalNone, RemoveCVReference<U>>)
explicit(!IsConvertible<U&&, JS::PropertyKey>) Optional(U&& value)
requires(!IsSame<RemoveCVReference<U>, Optional<JS::PropertyKey>> && IsConstructible<JS::PropertyKey, U &&>)
: m_value(forward<U>(value))
{
}
template<SameAs<OptionalNone> V>
Optional& operator=(V)
{
clear();
return *this;
}
Optional& operator=(Optional const& other)
{
if (this != &other) {
clear();
m_value = other.m_value;
}
return *this;
}
Optional& operator=(Optional&& other)
{
if (this != &other) {
clear();
m_value = other.m_value;
}
return *this;
}
void clear()
{
m_value = JS::PropertyKey { JS::PropertyKey::ShouldMakeEmptyOptional::Indeed };
}
[[nodiscard]] bool has_value() const
{
return !m_value.is_empty_optional();
}
[[nodiscard]] JS::PropertyKey& value() &
{
VERIFY(has_value());
return m_value;
}
[[nodiscard]] JS::PropertyKey const& value() const&
{
VERIFY(has_value());
return m_value;
}
[[nodiscard]] JS::PropertyKey value() &&
{
return release_value();
}
[[nodiscard]] JS::PropertyKey release_value()
{
VERIFY(has_value());
JS::PropertyKey released_value = m_value;
clear();
return released_value;
}
private:
JS::PropertyKey m_value { JS::PropertyKey::ShouldMakeEmptyOptional::Indeed };
using SentinelOptional::SentinelOptional;
};
}