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