chromium/chromium-65.0.3325.146-Implement-value-forward-constructor.patch
2018-03-15 12:17:21 -04:00

73 lines
3.2 KiB
Diff

diff -up chromium-65.0.3325.146/base/optional.h.vforward chromium-65.0.3325.146/base/optional.h
--- chromium-65.0.3325.146/base/optional.h.vforward 2018-03-13 22:35:46.383359966 -0400
+++ chromium-65.0.3325.146/base/optional.h 2018-03-13 22:37:48.724992995 -0400
@@ -354,6 +354,10 @@ struct IsConvertibleFromOptional
std::is_convertible<Optional<U>&&, T>::value ||
std::is_convertible<const Optional<U>&&, T>::value> {};
+// Forward compatibility for C++20.
+template <typename T>
+using RemoveCvRefT = std::remove_cv_t<std::remove_reference_t<T>>;
+
} // namespace internal
// base::Optional is a Chromium version of the C++17 optional class:
@@ -367,6 +371,13 @@ struct IsConvertibleFromOptional
// - 'constexpr' might be missing in some places for reasons specified locally.
// - No exceptions are thrown, because they are banned from Chromium.
// - All the non-members are in the 'base' namespace instead of 'std'.
+//
+// Note that T cannot have a constructor T(Optional<T>) etc. Optional<T> checks
+// T's constructor (specifically via IsConvertibleFromOptional), and in the
+// check whether T can be constructible from Optional<T>, which is recursive
+// so it does not work. As of Feb 2018, std::optional C++17 implementation in
+// both clang and gcc has same limitation. MSVC SFINAE looks to have different
+// behavior, but anyway it reports an error, too.
template <typename T>
class Optional
: public internal::OptionalBase<T>,
@@ -426,12 +437,6 @@ class Optional
explicit Optional(Optional<U>&& other)
: internal::OptionalBase<T>(std::move(other)) {}
- constexpr Optional(const T& value)
- : internal::OptionalBase<T>(in_place, value) {}
-
- constexpr Optional(T&& value)
- : internal::OptionalBase<T>(in_place, std::move(value)) {}
-
template <class... Args>
constexpr explicit Optional(in_place_t, Args&&... args)
: internal::OptionalBase<T>(in_place, std::forward<Args>(args)...) {}
@@ -447,6 +452,30 @@ class Optional
Args&&... args)
: internal::OptionalBase<T>(in_place, il, std::forward<Args>(args)...) {}
+ // Forward value constructor. Similar to converting constructors,
+ // conditionally explicit.
+ template <
+ typename U = value_type,
+ std::enable_if_t<
+ std::is_constructible<T, U&&>::value &&
+ !std::is_same<internal::RemoveCvRefT<U>, in_place_t>::value &&
+ !std::is_same<internal::RemoveCvRefT<U>, Optional<T>>::value &&
+ std::is_convertible<U&&, T>::value,
+ bool> = false>
+ constexpr Optional(U&& value)
+ : internal::OptionalBase<T>(in_place, std::forward<U>(value)) {}
+
+ template <
+ typename U = value_type,
+ std::enable_if_t<
+ std::is_constructible<T, U&&>::value &&
+ !std::is_same<internal::RemoveCvRefT<U>, in_place_t>::value &&
+ !std::is_same<internal::RemoveCvRefT<U>, Optional<T>>::value &&
+ !std::is_convertible<U&&, T>::value,
+ bool> = false>
+ constexpr explicit Optional(U&& value)
+ : internal::OptionalBase<T>(in_place, std::forward<U>(value)) {}
+
~Optional() = default;
// Defer copy-/move- assign operator implementation to OptionalBase.