--- /dev/null
+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <iterator>
+#include <memory>
+
+/*
+ * Similar to Python's enumerate(), folly::enumerate() can be used to
+ * iterate a range with a for-range loop, and it also allows to
+ * retrieve the count of iterations so far.
+ *
+ * For example:
+ *
+ * for (auto it : folly::enumerate(vec)) {
+ * // *it is a reference to the current element. Const if vec is const.
+ * // it->member can be used as well.
+ * // it.index contains the iteration count.
+ * }
+ *
+ * If the iteration variable is const, the reference is too.
+ *
+ * for (const auto it : folly::enumerate(vec)) {
+ * // *it is always a const reference.
+ * }
+ *
+ * @author Giuseppe Ottaviano <ott@fb.com>
+ */
+
+namespace folly {
+
+namespace detail {
+
+template <class T>
+struct MakeConst {
+ using type = const T;
+};
+template <class T>
+struct MakeConst<T&> {
+ using type = const T&;
+};
+template <class T>
+struct MakeConst<T*> {
+ using type = const T*;
+};
+
+template <class Iterator>
+class Enumerator {
+ public:
+ explicit Enumerator(Iterator it) : it_(std::move(it)) {}
+
+ class Proxy {
+ public:
+ using difference_type = ssize_t;
+ using value_type = typename std::iterator_traits<Iterator>::value_type;
+ using reference = typename std::iterator_traits<Iterator>::reference;
+ using pointer = typename std::iterator_traits<Iterator>::pointer;
+ using iterator_category = std::input_iterator_tag;
+
+ explicit Proxy(const Enumerator* e) : it_(e->it_), index(e->idx_) {}
+
+ // Non-const Proxy: Forward constness from Iterator.
+ reference operator*() {
+ return *it_;
+ }
+ pointer operator->() {
+ return std::addressof(**this);
+ }
+
+ // Const Proxy: Force const references.
+ typename MakeConst<reference>::type operator*() const {
+ return *it_;
+ }
+ typename MakeConst<pointer>::type operator->() const {
+ return std::addressof(**this);
+ }
+
+ private:
+ const Iterator& it_;
+
+ public:
+ const size_t index;
+ };
+
+ Proxy operator*() const {
+ return Proxy(this);
+ }
+
+ Enumerator& operator++() {
+ ++it_;
+ ++idx_;
+ return *this;
+ }
+
+ bool operator==(const Enumerator& rhs) {
+ return it_ == rhs.it_;
+ }
+
+ bool operator!=(const Enumerator& rhs) {
+ return !(*this == rhs);
+ }
+
+ private:
+ Iterator it_;
+ size_t idx_ = 0;
+};
+
+template <class Range>
+class RangeEnumerator {
+ Range r_;
+ using Iterator = decltype(r_.begin());
+
+ public:
+ explicit RangeEnumerator(Range&& r) : r_(std::forward<Range>(r)) {}
+
+ Enumerator<Iterator> begin() {
+ return Enumerator<Iterator>(r_.begin());
+ }
+ Enumerator<Iterator> end() {
+ return Enumerator<Iterator>(r_.end());
+ }
+};
+
+} // namespace detail
+
+template <class Range>
+detail::RangeEnumerator<Range> enumerate(Range&& r) {
+ return detail::RangeEnumerator<Range>(std::forward<Range>(r));
+}
+
+} // namespace folly
--- /dev/null
+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * 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.
+ */
+
+#include <string>
+#include <vector>
+
+#include <folly/Enumerate.h>
+#include <folly/Range.h>
+#include <gtest/gtest.h>
+
+TEST(Enumerate, Basic) {
+ std::vector<std::string> v = {"abc", "a", "ab"};
+ size_t i = 0;
+ for (auto it : folly::enumerate(v)) {
+ EXPECT_EQ(it.index, i);
+ EXPECT_EQ(*it, v[i]);
+ EXPECT_EQ(it->size(), v[i].size());
+
+ // Test mutability.
+ std::string newValue = "x";
+ *it = newValue;
+ EXPECT_EQ(newValue, v[i]);
+
+ ++i;
+ }
+
+ EXPECT_EQ(i, v.size());
+}
+
+TEST(Enumerate, Temporary) {
+ std::vector<std::string> v = {"abc", "a", "ab"};
+ size_t i = 0;
+ for (auto it : folly::enumerate(decltype(v)(v))) { // Copy v.
+ EXPECT_EQ(it.index, i);
+ EXPECT_EQ(*it, v[i]);
+ EXPECT_EQ(it->size(), v[i].size());
+ ++i;
+ }
+
+ EXPECT_EQ(i, v.size());
+};
+
+template <class T>
+struct IsConstReference {
+ constexpr static bool value = false;
+};
+template <class T>
+struct IsConstReference<const T&> {
+ constexpr static bool value = true;
+};
+
+TEST(Enumerate, BasicConstArg) {
+ const std::vector<std::string> v = {"abc", "a", "ab"};
+ size_t i = 0;
+ for (auto it : folly::enumerate(v)) {
+ static_assert(
+ IsConstReference<decltype(*it)>::value, "Enumerating a const vector");
+ EXPECT_EQ(it.index, i);
+ EXPECT_EQ(*it, v[i]);
+ EXPECT_EQ(it->size(), v[i].size());
+ ++i;
+ }
+
+ EXPECT_EQ(i, v.size());
+}
+
+TEST(Enumerate, BasicConstEnumerate) {
+ std::vector<std::string> v = {"abc", "a", "ab"};
+ size_t i = 0;
+ for (const auto it : folly::enumerate(v)) {
+ static_assert(IsConstReference<decltype(*it)>::value, "Const enumeration");
+ EXPECT_EQ(it.index, i);
+ EXPECT_EQ(*it, v[i]);
+ EXPECT_EQ(it->size(), v[i].size());
+ ++i;
+ }
+
+ EXPECT_EQ(i, v.size());
+}
+
+TEST(Enumerate, TemporaryConstEnumerate) {
+ std::vector<std::string> v = {"abc", "a", "ab"};
+ size_t i = 0;
+ for (const auto it : folly::enumerate(decltype(v)(v))) { // Copy v.
+ static_assert(IsConstReference<decltype(*it)>::value, "Const enumeration");
+ EXPECT_EQ(it.index, i);
+ EXPECT_EQ(*it, v[i]);
+ EXPECT_EQ(it->size(), v[i].size());
+ ++i;
+ }
+
+ EXPECT_EQ(i, v.size());
+}
+
+TEST(Enumerate, RangeSupport) {
+ std::vector<std::string> v = {"abc", "a", "ab"};
+ size_t i = 0;
+ for (const auto it : folly::enumerate(folly::range(v))) {
+ EXPECT_EQ(it.index, i);
+ EXPECT_EQ(*it, v[i]);
+ EXPECT_EQ(it->size(), v[i].size());
+ ++i;
+ }
+
+ EXPECT_EQ(i, v.size());
+}
+
+TEST(Enumerate, EmptyRange) {
+ std::vector<std::string> v;
+ for (auto it : folly::enumerate(v)) {
+ (void)it; // Silence warnings.
+ EXPECT_TRUE(false);
+ }
+}
projects / folly.git / commitdiff