Example implementation of enumerate

cpp/arcticdb/CMakeLists.txt

@@ -464,7 +464,7 @@ set(arcticdb_srcs
         version/version_utils.cpp
         version/symbol_list.cpp
         version/version_map_batch_methods.cpp
-)
+        util/enumerate.hpp)
 
 if(${ARCTICDB_INCLUDE_ROCKSDB})
     list (APPEND arcticdb_srcs
@@ -815,7 +815,7 @@ if(${TEST})
             version/test/test_sorting_info_state_machine.cpp
             version/test/version_map_model.hpp
             storage/test/common.hpp
-    )
+            util/test/test_enumerate.cpp)
 
     set(EXECUTABLE_PERMS OWNER_WRITE OWNER_READ OWNER_EXECUTE GROUP_READ GROUP_EXECUTE WORLD_READ WORLD_EXECUTE) # 755
 

cpp/arcticdb/util/enumerate.hpp

@@ -0,0 +1,114 @@
+#pragma once
+
+// An internal implementation of folly's enumerate: https://github.com/facebook/folly/blob/main/folly/container/Enumerate.h
+
+#include <iterator>
+#include <memory>
+
+#include <arcticdb/util/preprocess.hpp>
+
+namespace arcticdb {
+
+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:
+    constexpr 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;
+
+        ARCTICDB_FORCE_INLINE constexpr explicit Proxy(const Enumerator& enumerator)
+            : index(enumerator.idx_), element(*enumerator.it_) {}
+
+        ARCTICDB_FORCE_INLINE constexpr reference operator*() { return element; }
+        ARCTICDB_FORCE_INLINE constexpr pointer operator->() {
+            return std::addressof(element);
+        }
+
+        ARCTICDB_FORCE_INLINE constexpr typename MakeConst<reference>::type
+        operator*() const {
+            return element;
+        }
+        ARCTICDB_FORCE_INLINE constexpr typename MakeConst<pointer>::type operator->()
+        const {
+            return std::addressof(element);
+        }
+
+    public:
+        const size_t index;
+        reference element;
+    };
+
+    ARCTICDB_FORCE_INLINE constexpr Proxy operator*() const { return Proxy(*this); }
+
+    ARCTICDB_FORCE_INLINE constexpr Enumerator& operator++() {
+        ++it_;
+        ++idx_;
+        return *this;
+    }
+
+    template <typename OtherIterator>
+    ARCTICDB_FORCE_INLINE constexpr bool operator==(
+        const Enumerator<OtherIterator>& rhs) const {
+        return it_ == rhs.it_;
+    }
+
+    template <typename OtherIterator>
+    ARCTICDB_FORCE_INLINE constexpr bool operator!=(
+        const Enumerator<OtherIterator>& rhs) const {
+        return !(it_ == rhs.it_);
+    }
+
+private:
+    template <typename OtherIterator>
+    friend class Enumerator;
+
+    Iterator it_;
+    size_t idx_ = 0;
+};
+
+template <class RangeType>
+class RangeEnumerator {
+    RangeType r_;
+    using BeginIteratorType = decltype(std::declval<RangeType>().begin());
+    using EndIteratorType = decltype(std::declval<RangeType>().end());
+
+public:
+    constexpr explicit RangeEnumerator(RangeType&& r) : r_(std::forward<RangeType>(r)) {}
+
+    constexpr Enumerator<BeginIteratorType> begin() {
+        return Enumerator<BeginIteratorType>(r_.begin());
+    }
+    constexpr Enumerator<EndIteratorType> end() {
+        return Enumerator<EndIteratorType>(r_.end());
+    }
+};
+
+} // namespace detail
+
+template <class RangeType>
+constexpr detail::RangeEnumerator<RangeType> enumerate(RangeType&& r) {
+    return detail::RangeEnumerator<RangeType>(std::forward<RangeType>(r));
+}
+
+} // namespace arcticdb

cpp/arcticdb/util/preprocess.hpp

@@ -26,3 +26,9 @@
 #define ARCTICDB_LIKELY
 #define ARCTICDB_UNLIKELY
 #endif
+
+#ifdef _MSC_VER
+#define ARCTICDB_FORCE_INLINE __forceinline
+#elif defined(__GNUC__)
+#define ARCTICDB_FORCE_INLINE inline __attribute__((__always_inline__))
+#else

cpp/arcticdb/util/test/test_enumerate.cpp

@@ -0,0 +1,14 @@
+#include <gtest/gtest.h>
+#include <arcticdb/util/enumerate.hpp>
+#include <arcticdb/log/log.hpp>
+
+TEST(Enumerate, Vector) {
+    std::vector<int> vec = {1, 2, 3, 4};
+
+    using namespace arcticdb;
+
+    for(auto&& [thing, index] : enumerate(vec)) {
+        arcticdb::log::version().info("{} : {}", thing, index);
+    }
+}
+