Add key-only projections to immutable C++ maps (#1166)

* Add a simple range adapter.
* Add SortedMap::keys
* Add SortedMap::keys_from
* Add SortedMap::keys_in

3 files changed, 81 insertions, 0 deletions

diff --git a/Firestore/core/src/firebase/firestore/util/CMakeLists.txt b/Firestore/core/src/firebase/firestore/util/CMakeLists.txt
index 701d288..3afead1 100644
--- a/Firestore/core/src/firebase/firestore/util/CMakeLists.txt
+++ b/Firestore/core/src/firebase/firestore/util/CMakeLists.txt
@@ -131,6 +131,7 @@ cc_library(
     iterator_adaptors.h
     ordered_code.cc
     ordered_code.h
+    range.h
     secure_random.h
     status.cc
     status.h
diff --git a/Firestore/core/src/firebase/firestore/util/comparator_holder.h b/Firestore/core/src/firebase/firestore/util/comparator_holder.h
index c7f6144..3147117 100644
--- a/Firestore/core/src/firebase/firestore/util/comparator_holder.h
+++ b/Firestore/core/src/firebase/firestore/util/comparator_holder.h
@@ -35,6 +35,7 @@ class ComparatorHolder {
       : comparator_(comparator) {
   }
 
+ public:
   const C& comparator() const noexcept {
     return comparator_;
   }
@@ -50,6 +51,7 @@ class ComparatorHolder<C, true> : private C {
   explicit ComparatorHolder(const C& /* comparator */) noexcept {
   }
 
+ public:
   const C& comparator() const noexcept {
     return *this;
   }
diff --git a/Firestore/core/src/firebase/firestore/util/range.h b/Firestore/core/src/firebase/firestore/util/range.h
new file mode 100644
index 0000000..9e96c67
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/util/range.h
@@ -0,0 +1,78 @@
+/*
+ * 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_RANGE_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_RANGE_H_
+
+#include <iterator>
+#include <utility>
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+/**
+ * Adapts a pair of iterators into a range suitable for use with range-based
+ * for loops.
+ */
+template <typename Iterator>
+class range {
+ public:
+  using value_type = typename std::iterator_traits<Iterator>::value_type;
+  using iterator = Iterator;
+  using const_iterator = Iterator;
+
+  /**
+   * Default range which constructs default begin and end pointers. For most
+   * implementations where the end pointer is a null pointer or some other
+   * default value, this ends up constructing the empty range.
+   */
+  range() : begin_{}, end_{} {
+  }
+
+  /**
+   * Creates a half-open range starting from begin up to, but not including end.
+   */
+  range(iterator&& begin, iterator&& end)
+      : begin_{std::move(begin)}, end_{std::move(end)} {
+  }
+
+  iterator begin() const {
+    return begin_;
+  }
+
+  iterator end() const {
+    return end_;
+  }
+
+ private:
+  Iterator begin_;
+  Iterator end_;
+};
+
+/**
+ * Creates ranges with type deduction.
+ */
+template <typename Iterator>
+range<Iterator> make_range(Iterator begin, Iterator end) {
+  return range<Iterator>{std::move(begin), std::move(end)};
+}
+
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_RANGE_H_