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diff -up chromium-65.0.3325.146/base/optional.h.converting chromium-65.0.3325.146/base/optional.h
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--- chromium-65.0.3325.146/base/optional.h.converting 2018-03-13 22:31:05.248797490 -0400
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+++ chromium-65.0.3325.146/base/optional.h 2018-03-13 22:33:10.826368771 -0400
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@@ -31,6 +31,10 @@ constexpr in_place_t in_place = {};
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// http://en.cppreference.com/w/cpp/utility/optional/nullopt
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constexpr nullopt_t nullopt(0);
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+// Forward declaration, which is refered by following helpers.
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+template <typename T>
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+class Optional;
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+
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namespace internal {
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template <typename T, bool = std::is_trivially_destructible<T>::value>
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@@ -220,6 +224,19 @@ class OptionalBase {
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constexpr explicit OptionalBase(in_place_t, Args&&... args)
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: storage_(in_place, std::forward<Args>(args)...) {}
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+ // Implementation of converting constructors.
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+ template <typename U>
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+ explicit OptionalBase(const OptionalBase<U>& other) {
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+ if (other.storage_.is_populated_)
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+ storage_.Init(other.storage_.value_);
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+ }
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+
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+ template <typename U>
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+ explicit OptionalBase(OptionalBase<U>&& other) {
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+ if (other.storage_.is_populated_)
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+ storage_.Init(std::move(other.storage_.value_));
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+ }
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+
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~OptionalBase() = default;
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OptionalBase& operator=(const OptionalBase& other) {
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@@ -263,6 +280,11 @@ class OptionalBase {
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storage_.is_populated_ = false;
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}
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+ // For implementing conversion, allow access to other typed OptionalBase
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+ // class.
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+ template <typename U>
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+ friend class OptionalBase;
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+
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OptionalStorage<T> storage_;
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};
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@@ -318,6 +340,20 @@ struct MoveAssignable<false> {
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MoveAssignable& operator=(MoveAssignable&&) = delete;
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};
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+// Helper to conditionally enable converting constructors.
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+template <typename T, typename U>
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+struct IsConvertibleFromOptional
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+ : std::integral_constant<
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+ bool,
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+ std::is_constructible<T, Optional<U>&>::value ||
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+ std::is_constructible<T, const Optional<U>&>::value ||
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+ std::is_constructible<T, Optional<U>&&>::value ||
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+ std::is_constructible<T, const Optional<U>&&>::value ||
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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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+ std::is_convertible<Optional<U>&&, T>::value ||
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+ std::is_convertible<const Optional<U>&&, T>::value> {};
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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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@@ -348,7 +384,47 @@ class Optional
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constexpr Optional(const Optional& other) = default;
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constexpr Optional(Optional&& other) = default;
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- constexpr Optional(nullopt_t) {}
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+ constexpr Optional(nullopt_t) {} // NOLINT(runtime/explicit)
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+
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+ // Converting copy constructor. "explicit" only if
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+ // std::is_convertible<const U&, T>::value is false. It is implemented by
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+ // declaring two almost same constructors, but that condition in enable_if_t
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+ // is different, so that either one is chosen, thanks to SFINAE.
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+ template <
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+ typename U,
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+ std::enable_if_t<std::is_constructible<T, const U&>::value &&
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+ !internal::IsConvertibleFromOptional<T, U>::value &&
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+ std::is_convertible<const U&, T>::value,
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+ bool> = false>
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+ Optional(const Optional<U>& other) : internal::OptionalBase<T>(other) {}
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+
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+ template <
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+ typename U,
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+ std::enable_if_t<std::is_constructible<T, const U&>::value &&
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+ !internal::IsConvertibleFromOptional<T, U>::value &&
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+ !std::is_convertible<const U&, T>::value,
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+ bool> = false>
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+ explicit Optional(const Optional<U>& other)
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+ : internal::OptionalBase<T>(other) {}
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+
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+ // Converting move constructor. Similar to converting copy constructor,
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+ // declaring two (explicit and non-explicit) constructors.
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+ template <
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+ typename U,
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+ std::enable_if_t<std::is_constructible<T, U&&>::value &&
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+ !internal::IsConvertibleFromOptional<T, U>::value &&
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+ std::is_convertible<U&&, T>::value,
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+ bool> = false>
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+ Optional(Optional<U>&& other) : internal::OptionalBase<T>(std::move(other)) {}
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+
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+ template <
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+ typename U,
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+ std::enable_if_t<std::is_constructible<T, U&&>::value &&
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+ !internal::IsConvertibleFromOptional<T, U>::value &&
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+ !std::is_convertible<U&&, T>::value,
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+ bool> = false>
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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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