Update (non-copy, non-move) assign operators.
Fix perfect-forwarded assign operator to look at condition to
decide whether it should participate in overload resolution.
Add Optional<U> copy- and move-like assign operators.
For that implementation, OptionalBase's copy-/move-assign
operators are slightly refactored.
BUG=784732
TEST=Ran trybot.
Change-Id: I69db9def857a1cce8e7b05f0c6e11922ee8d95db
Reviewed-on: https://chromium-review.googlesource.com/856539
Reviewed-by: danakj <[email protected]>
Commit-Queue: Hidehiko Abe <[email protected]>
Cr-Commit-Position: refs/heads/master@{#538699}diff --git a/base/optional.h b/base/optional.h
index 9599baf..d65881b 100644
--- a/base/optional.h
+++ b/base/optional.h
@@ -239,37 +239,37 @@
~OptionalBase() = default;
OptionalBase& operator=(const OptionalBase& other) {
- if (!other.storage_.is_populated_) {
- FreeIfNeeded();
- return *this;
- }
-
- InitOrAssign(other.storage_.value_);
+ CopyAssign(other);
return *this;
}
OptionalBase& operator=(OptionalBase&& other) {
- if (!other.storage_.is_populated_) {
- FreeIfNeeded();
- return *this;
- }
-
- InitOrAssign(std::move(other.storage_.value_));
+ MoveAssign(std::move(other));
return *this;
}
- void InitOrAssign(const T& value) {
- if (!storage_.is_populated_)
- storage_.Init(value);
+ template <typename U>
+ void CopyAssign(const OptionalBase<U>& other) {
+ if (other.storage_.is_populated_)
+ InitOrAssign(other.storage_.value_);
else
- storage_.value_ = value;
+ FreeIfNeeded();
}
- void InitOrAssign(T&& value) {
- if (!storage_.is_populated_)
- storage_.Init(std::move(value));
+ template <typename U>
+ void MoveAssign(OptionalBase<U>&& other) {
+ if (other.storage_.is_populated_)
+ InitOrAssign(std::move(other.storage_.value_));
else
- storage_.value_ = std::move(value);
+ FreeIfNeeded();
+ }
+
+ template <typename U>
+ void InitOrAssign(U&& value) {
+ if (storage_.is_populated_)
+ storage_.value_ = std::forward<U>(value);
+ else
+ storage_.Init(std::forward<U>(value));
}
void FreeIfNeeded() {
@@ -339,7 +339,7 @@
MoveAssignable& operator=(MoveAssignable&&) = delete;
};
-// Helper to conditionally enable converting constructors.
+// Helper to conditionally enable converting constructors and assign operators.
template <typename T, typename U>
struct IsConvertibleFromOptional
: std::integral_constant<
@@ -353,6 +353,16 @@
std::is_convertible<Optional<U>&&, T>::value ||
std::is_convertible<const Optional<U>&&, T>::value> {};
+template <typename T, typename U>
+struct IsAssignableFromOptional
+ : std::integral_constant<
+ bool,
+ IsConvertibleFromOptional<T, U>::value ||
+ std::is_assignable<T&, Optional<U>&>::value ||
+ std::is_assignable<T&, const Optional<U>&>::value ||
+ std::is_assignable<T&, Optional<U>&&>::value ||
+ std::is_assignable<T&, const Optional<U>&&>::value> {};
+
// Forward compatibility for C++20.
template <typename T>
using RemoveCvRefT = std::remove_cv_t<std::remove_reference_t<T>>;
@@ -486,14 +496,42 @@
return *this;
}
- template <class U>
- typename std::enable_if<std::is_same<std::decay_t<U>, T>::value,
- Optional&>::type
+ // Perfect-forwarded assignment.
+ template <typename U>
+ std::enable_if_t<
+ !std::is_same<internal::RemoveCvRefT<U>, Optional<T>>::value &&
+ std::is_constructible<T, U>::value &&
+ std::is_assignable<T&, U>::value &&
+ (!std::is_scalar<T>::value ||
+ !std::is_same<std::decay_t<U>, T>::value),
+ Optional&>
operator=(U&& value) {
InitOrAssign(std::forward<U>(value));
return *this;
}
+ // Copy assign the state of other.
+ template <typename U>
+ std::enable_if_t<!internal::IsAssignableFromOptional<T, U>::value &&
+ std::is_constructible<T, const U&>::value &&
+ std::is_assignable<T&, const U&>::value,
+ Optional&>
+ operator=(const Optional<U>& other) {
+ CopyAssign(other);
+ return *this;
+ }
+
+ // Move assign the state of other.
+ template <typename U>
+ std::enable_if_t<!internal::IsAssignableFromOptional<T, U>::value &&
+ std::is_constructible<T, U>::value &&
+ std::is_assignable<T&, U>::value,
+ Optional&>
+ operator=(Optional<U>&& other) {
+ MoveAssign(std::move(other));
+ return *this;
+ }
+
constexpr const T* operator->() const {
DCHECK(storage_.is_populated_);
return &value();
@@ -605,8 +643,10 @@
private:
// Accessing template base class's protected member needs explicit
// declaration to do so.
+ using internal::OptionalBase<T>::CopyAssign;
using internal::OptionalBase<T>::FreeIfNeeded;
using internal::OptionalBase<T>::InitOrAssign;
+ using internal::OptionalBase<T>::MoveAssign;
using internal::OptionalBase<T>::storage_;
};
