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Diffstat (limited to 'Firestore/core/src/firebase/firestore/util/comparator_holder.h')
-rw-r--r-- | Firestore/core/src/firebase/firestore/util/comparator_holder.h | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/Firestore/core/src/firebase/firestore/util/comparator_holder.h b/Firestore/core/src/firebase/firestore/util/comparator_holder.h new file mode 100644 index 0000000..8641b0f --- /dev/null +++ b/Firestore/core/src/firebase/firestore/util/comparator_holder.h @@ -0,0 +1,62 @@ +/* + * Copyright 2018 Google + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_COMPARATOR_HOLDER_H_ +#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_COMPARATOR_HOLDER_H_ + +#include <type_traits> + +namespace firebase { +namespace firestore { +namespace util { + +/** + * A holder of some comparator (e.g. std::less or util::Comparator) that + * implements the empty base optimization for the common case where the + * comparator occupies no storage. + */ +template <typename C, bool = std::is_empty<C>::value> +class ComparatorHolder { + protected: + explicit ComparatorHolder(const C& comparator) noexcept + : comparator_(comparator) { + } + + const C& comparator() const noexcept { + return comparator_; + } + + private: + C comparator_; +}; + +// Implementation to use when C is empty. +template <typename C> +class ComparatorHolder<C, true> : private C { + protected: + explicit ComparatorHolder(const C&) noexcept { + } + + const C& comparator() const noexcept { + return *this; + } +}; + +} // namespace util +} // namespace firestore +} // namespace firebase + +#endif // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_COMPARATOR_HOLDER_H_ |