зеркало из https://github.com/mozilla/gecko-dev.git
119 строки
3.1 KiB
C++
119 строки
3.1 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef DOM_QUOTA_FLATTEN_H_
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#define DOM_QUOTA_FLATTEN_H_
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#include <iterator>
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#include <type_traits>
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#include <utility>
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// XXX This should be moved to MFBT.
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namespace mozilla::dom::quota {
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namespace detail {
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using std::begin;
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using std::end;
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template <typename T, typename NestedRange>
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auto Flatten(NestedRange&& aRange) -> std::enable_if_t<
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std::is_same_v<T, std::decay_t<typename decltype(begin(
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std::declval<const NestedRange&>()))::value_type>>,
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std::conditional_t<std::is_rvalue_reference_v<NestedRange>,
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std::decay_t<NestedRange>, NestedRange>> {
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return std::forward<NestedRange>(aRange);
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}
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template <typename T, typename NestedRange>
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struct FlatIter {
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using OuterIterator =
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decltype(begin(std::declval<const std::decay_t<NestedRange>&>()));
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using InnerIterator =
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decltype(begin(*begin(std::declval<const std::decay_t<NestedRange>&>())));
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explicit FlatIter(const NestedRange& aRange, OuterIterator aIter)
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: mOuterIter{std::move(aIter)}, mOuterEnd{end(aRange)} {
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InitInner();
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}
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const T& operator*() const { return *mInnerIter; }
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FlatIter& operator++() {
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++mInnerIter;
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if (mInnerIter == mInnerEnd) {
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++mOuterIter;
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InitInner();
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}
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return *this;
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}
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bool operator!=(const FlatIter& aOther) const {
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return mOuterIter != aOther.mOuterIter ||
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(mOuterIter != mOuterEnd && mInnerIter != aOther.mInnerIter);
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}
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private:
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void InitInner() {
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while (mOuterIter != mOuterEnd) {
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const typename OuterIterator::value_type& innerRange = *mOuterIter;
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mInnerIter = begin(innerRange);
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mInnerEnd = end(innerRange);
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if (mInnerIter != mInnerEnd) {
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break;
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}
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++mOuterIter;
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}
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}
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OuterIterator mOuterIter;
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const OuterIterator mOuterEnd;
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InnerIterator mInnerIter;
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InnerIterator mInnerEnd;
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};
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template <typename T, typename NestedRange>
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struct FlatRange {
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explicit FlatRange(NestedRange aRange) : mRange{std::move(aRange)} {}
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auto begin() const {
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using std::begin;
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return FlatIter<T, NestedRange>{mRange, begin(mRange)};
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}
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auto end() const {
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using std::end;
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return FlatIter<T, NestedRange>{mRange, end(mRange)};
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}
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private:
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NestedRange mRange;
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};
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template <typename T, typename NestedRange>
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auto Flatten(NestedRange&& aRange) -> std::enable_if_t<
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!std::is_same_v<
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T, std::decay_t<typename decltype(begin(
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std::declval<const std::decay_t<NestedRange>&>()))::value_type>>,
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FlatRange<T, NestedRange>> {
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return FlatRange<T, NestedRange>{std::forward<NestedRange>(aRange)};
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}
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} // namespace detail
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template <typename T, typename NestedRange>
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auto Flatten(NestedRange&& aRange) -> decltype(auto) {
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return detail::Flatten<T>(std::forward<NestedRange>(aRange));
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}
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} // namespace mozilla::dom::quota
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#endif
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