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TM::Optional: Run destructor when clearing the value #2860

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TM::Optional: Run destructor when clearing the value #2860

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4071345
TM::Optional: Remove unused header stdio.h
herwinw Dec 20, 2025
4169744
TM::Optional: Run destructor when clearing the value
herwinw Nov 29, 2025
9880ad0
TM::Optional: Support trivially copyable operations
herwinw Dec 20, 2025
791b16e
TM::Optional: Guard for copy assignment with self
herwinw Dec 20, 2025
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79 changes: 56 additions & 23 deletions ext/tm/include/tm/optional.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

#include <assert.h>
#include <functional>
#include <stdio.h>
#include <string.h>
#include <utility>

namespace TM {
Expand All @@ -20,8 +20,9 @@ class Optional {
* ```
*/
Optional(const T &value)
: m_present { true }
, m_value { value } { }
: m_present { true } {
new (m_value) T { value };
}

/**
* Constructs a new Optional with a value.
Expand All @@ -33,8 +34,9 @@ class Optional {
* ```
*/
Optional(T &&value)
: m_present { true }
, m_value { std::move(value) } { }
: m_present { true } {
new (m_value) T { std::move(value) };
}

/**
* Constructs a new Optional without a value.
Expand All @@ -61,7 +63,7 @@ class Optional {
Optional(const Optional &other)
: m_present { other.m_present } {
if (m_present)
m_value = other.m_value;
*reinterpret_cast<T *>(m_value) = *reinterpret_cast<const T *>(other.m_value);
}

/**
Expand All @@ -75,11 +77,16 @@ class Optional {
* assert_eq(obj, opt2.value());
* ```
*/
Optional(Optional &&other)
: m_present { other.m_present } {
Optional(Optional &&other) {
m_present = other.m_present;
if (m_present) {
m_value = std::move(other.m_value);
other.m_present = false;
if constexpr (std::is_trivially_copyable_v<T>) {
memcpy(m_value, other.m_value, sizeof(m_value));
other.clear_after_trivial_copy();
} else {
*reinterpret_cast<T *>(m_value) = std::move(*reinterpret_cast<T *>(other.m_value));
other.clear();
}
}
}

Expand All @@ -101,9 +108,13 @@ class Optional {
* ```
*/
Optional<T> &operator=(const Optional<T> &other) {
if (this == &other)
return *this;
if (m_present)
clear();
m_present = other.m_present;
if (m_present)
m_value = other.m_value;
*reinterpret_cast<T *>(m_value) = *reinterpret_cast<const T *>(other.m_value);
return *this;
}

Expand All @@ -121,10 +132,19 @@ class Optional {
* ```
*/
Optional<T> &operator=(Optional<T> &&other) {
if (this == &other)
return *this;
if (m_present)
clear();
m_present = other.m_present;
if (m_present) {
m_value = std::move(other.m_value);
other.m_present = false;
if constexpr (std::is_trivially_copyable_v<T>) {
memcpy(m_value, other.m_value, sizeof(m_value));
other.clear_after_trivial_copy();
} else {
*reinterpret_cast<T *>(m_value) = std::move(*reinterpret_cast<const T *>(other.m_value));
other.clear();
}
}
return *this;
}
Expand All @@ -141,8 +161,10 @@ class Optional {
* ```
*/
Optional<T> &operator=(T &&value) {
if (m_present)
clear();
m_present = true;
m_value = std::move(value);
*reinterpret_cast<T *>(m_value) = std::move(value);
return *this;
}

Expand All @@ -164,7 +186,7 @@ class Optional {
*/
T &value() {
assert(m_present);
return m_value;
return *reinterpret_cast<T *>(m_value);
}

/**
Expand All @@ -185,7 +207,7 @@ class Optional {
*/
T const &value() const {
assert(m_present);
return m_value;
return *reinterpret_cast<const T *>(m_value);
}

/**
Expand Down Expand Up @@ -233,7 +255,7 @@ class Optional {
*/
T value_or(std::function<T()> fallback) const {
if (present())
return value();
return *reinterpret_cast<const T *>(m_value);
else
return fallback();
}
Expand All @@ -259,7 +281,7 @@ class Optional {
*/
T &operator*() {
assert(m_present);
return m_value;
return *reinterpret_cast<T *>(m_value);
}

/**
Expand All @@ -280,7 +302,7 @@ class Optional {
*/
T const &operator*() const {
assert(m_present);
return m_value;
return *reinterpret_cast<const T *>(m_value);
}

/**
Expand All @@ -301,7 +323,7 @@ class Optional {
*/
T *operator->() {
assert(m_present);
return &m_value;
return reinterpret_cast<T *>(m_value);
}

/**
Expand All @@ -322,7 +344,7 @@ class Optional {
*/
T const *operator->() const {
assert(m_present);
return &m_value;
return reinterpret_cast<const T *>(m_value);
}

/**
Expand All @@ -335,7 +357,13 @@ class Optional {
* assert_not(opt);
* ```
*/
void clear() { m_present = false; }
void clear() {
if (m_present) {
reinterpret_cast<T *>(m_value)->~T();
memset(m_value, 0, sizeof(m_value));
}
m_present = false;
}

/**
* Returns true if the Optional contains a value.
Expand All @@ -362,9 +390,14 @@ class Optional {
bool present() const { return m_present; }

private:
void clear_after_trivial_copy() {
m_present = false;
memset(m_value, 0, sizeof(m_value));
}

bool m_present;

T m_value {};
alignas(T) unsigned char m_value[sizeof(T)] {};
};

}
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