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Fix bugs in in ctl::optional

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Manually manage the lifetime of `value_` by using an anonymous
`union`. This fixes a bunch of double-frees and double-constructs.

Additionally move the `present_` flag last. When `T` has padding
`present_` will be placed there saving `alignof(T)` bytes from
`sizeof(optional<T>)`.
This commit is contained in:
Alkis Evlogimenos 2024-06-07 07:02:36 +00:00 • committed by Alkis Evlogimenos
parent 2ba6b0158f
commit 5e0de0d75d
1 changed files with 23 additions and 12 deletions
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35
ctl/optional.h
View file

@ -14,38 +14,45 @@ class optional
public:
using value_type = T;
~optional() = default;
~optional()
{
if (present_)
value_.~T();
}
optional() noexcept : present_(false)
{
}
optional(const T& value) : present_(true), value_(value)
optional(const T& value) : present_(true)
{
new (&value_) T(value);
}
optional(T&& value) : present_(true), value_(std::move(value))
optional(T&& value) : present_(true)
{
new (&value_) T(std::move(value));
}
optional(const optional& other) : present_(other.present_)
{
if (present_)
if (other.present_)
new (&value_) T(other.value_);
}
optional(optional&& other) noexcept : present_(other.present_)
{
if (present_)
value_ = std::move(other.value_);
if (other.present_)
new (&value_) T(std::move(other.value_));
}
optional& operator=(const optional& other)
{
if (this != &other) {
reset();
if (other.present_)
new (&value_) T(other.value_);
present_ = other.present_;
if (present_)
value_ = other.value_;
}
return *this;
}
@ -53,9 +60,10 @@ class optional
optional& operator=(optional&& other) noexcept
{
if (this != &other) {
reset();
if (other.present_)
new (&value_) T(std::move(other.value_));
present_ = other.present_;
if (present_)
value_ = std::move(other.value_);
}
return *this;
}
@ -102,8 +110,9 @@ class optional
template<typename... Args>
void emplace(Args&&... args)
{
reset();
present_ = true;
value_ = T(std::forward<Args>(args)...);
new (&value_) T(std::forward<Args>(args)...);
}
void swap(optional& other) noexcept
@ -120,8 +129,10 @@ class optional
}
private:
union {
T value_;
};
bool present_;
T value_;
};
} // namespace ctl