4 files changed, 401 insertions, 0 deletions
diff --git a/absl/utility/BUILD.bazel b/absl/utility/BUILD.bazel
new file mode 100644
index 000000000000..73d051992bd3
--- /dev/null
+++ b/absl/utility/BUILD.bazel
@@ -0,0 +1,34 @@
+load(
+    "//absl:copts.bzl",
+    "ABSL_DEFAULT_COPTS",
+    "ABSL_TEST_COPTS",
+)
+load(
+    "//absl:test_dependencies.bzl",
+    "GUNIT_MAIN_DEPS_SELECTOR",
+)
+
+package(default_visibility = ["//visibility:public"])
+
+licenses(["unencumbered"])  # Owned by Google
+
+cc_library(
+    name = "utility",
+    srcs = ["utility.cc"],
+    hdrs = ["utility.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    deps = [
+        "//absl/base:config",
+        "//absl/meta:type_traits",
+    ],
+)
+
+cc_test(
+    name = "utility_test",
+    srcs = ["utility_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":utility",
+        "//absl/base:core_headers",
+    ] + select(GUNIT_MAIN_DEPS_SELECTOR),
+)
diff --git a/absl/utility/utility.cc b/absl/utility/utility.cc
new file mode 100644
index 000000000000..fce79f5bb5b8
--- /dev/null
+++ b/absl/utility/utility.cc
@@ -0,0 +1,27 @@
+// Copyright 2017 The Abseil Authors.
+//
+// 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.
+
+// -----------------------------------------------------------------------------
+// File: ascii.h
+// -----------------------------------------------------------------------------
+//
+#include "absl/utility/utility.h"
+
+namespace absl {
+
+#ifndef ABSL_HAVE_STD_OPTIONAL
+const in_place_t in_place{};
+#endif
+
+}  // namespace absl
diff --git a/absl/utility/utility.h b/absl/utility/utility.h
new file mode 100644
index 000000000000..4f4a0624d3db
--- /dev/null
+++ b/absl/utility/utility.h
@@ -0,0 +1,177 @@
+// Copyright 2017 The Abseil Authors.
+//
+// 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.
+//
+
+// absl/utility:utility is an extension of the <utility> header
+//
+// It provides stand-ins for C++14's std::integer_sequence and
+// related utilities. They are intended to be exactly equivalent.
+//   - integer_sequence<T, Ints...>  == std::integer_sequence<T, Ints...>
+//   - index_sequence<Ints...>       == std::index_sequence<Ints...>
+//   - make_integer_sequence<T, N>   == std::make_integer_sequence<T, N>
+//   - make_index_sequence<N>        == std::make_index_sequence<N>
+//   - index_sequence_for<Ts...>     == std::index_sequence_for<Ts...>
+//
+// It also provides the tag types in_place_t, in_place_type_t, and
+// in_place_index_t, as well as the constant in_place, and constexpr std::move
+// and std::forward impolementations in C++11.
+//
+// References:
+//  http://en.cppreference.com/w/cpp/utility/integer_sequence
+//  http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3658.html
+//
+// Example:
+//   // Unpack a tuple for use as a function call's argument list.
+//
+//   template <typename F, typename Tup, size_t... Is>
+//   auto Impl(F f, const Tup& tup, index_sequence<Is...>)
+//       -> decltype(f(std::get<Is>(tup) ...)) {
+//     return f(std::get<Is>(tup) ...);
+//   }
+//
+//   template <typename Tup>
+//   using TupIdxSeq = make_index_sequence<std::tuple_size<Tup>::value>;
+//
+//   template <typename F, typename Tup>
+//   auto ApplyFromTuple(F f, const Tup& tup)
+//       -> decltype(Impl(f, tup, TupIdxSeq<Tup>{})) {
+//     return Impl(f, tup, TupIdxSeq<Tup>{});
+//   }
+#ifndef ABSL_UTILITY_UTILITY_H_
+#define ABSL_UTILITY_UTILITY_H_
+
+#include <cstddef>
+#include <cstdlib>
+#include <utility>
+
+#include "absl/base/config.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+
+// Equivalent to std::integer_sequence.
+//
+// Function templates can deduce compile-time integer sequences by accepting
+// an argument of integer_sequence<T, Ints...>. This is a common need when
+// working with C++11 variadic templates.
+//
+// T       - the integer type of the sequence elements
+// ...Ints - a parameter pack of T values representing the sequence
+template <typename T, T... Ints>
+struct integer_sequence {
+  using value_type = T;
+  static constexpr size_t size() noexcept { return sizeof...(Ints); }
+};
+
+// Equivalent to std::index_sequence.
+//
+// Alias for an integer_sequence of size_t.
+template <size_t... Ints>
+using index_sequence = integer_sequence<size_t, Ints...>;
+
+namespace utility_internal {
+
+template <typename Seq, size_t SeqSize, size_t Rem>
+struct Extend;
+
+// Note that SeqSize == sizeof...(Ints). It's passed explicitly for efficiency.
+template <typename T, T... Ints, size_t SeqSize>
+struct Extend<integer_sequence<T, Ints...>, SeqSize, 0> {
+  using type = integer_sequence<T, Ints..., (Ints + SeqSize)...>;
+};
+
+template <typename T, T... Ints, size_t SeqSize>
+struct Extend<integer_sequence<T, Ints...>, SeqSize, 1> {
+  using type = integer_sequence<T, Ints..., (Ints + SeqSize)..., 2 * SeqSize>;
+};
+
+// Recursion helper for 'make_integer_sequence<T, N>'.
+// 'Gen<T, N>::type' is an alias for 'integer_sequence<T, 0, 1, ... N-1>'.
+template <typename T, size_t N>
+struct Gen {
+  using type =
+      typename Extend<typename Gen<T, N / 2>::type, N / 2, N % 2>::type;
+};
+
+template <typename T>
+struct Gen<T, 0> {
+  using type = integer_sequence<T>;
+};
+
+}  // namespace utility_internal
+
+// Compile-time sequences of integers
+
+// Equivalent to std::make_integer_sequence.
+//
+// make_integer_sequence<int, N> is integer_sequence<int, 0, 1, ..., N-1>;
+template <typename T, T N>
+using make_integer_sequence = typename utility_internal::Gen<T, N>::type;
+
+// Equivalent to std::make_index_sequence.
+//
+// make_index_sequence<N> is index_sequence<0, 1, ..., N-1>;
+template <size_t N>
+using make_index_sequence = make_integer_sequence<size_t, N>;
+
+// Equivalent to std::index_sequence_for.
+//
+// Convert a typename pack into an index sequence of the same length.
+template <typename... Ts>
+using index_sequence_for = make_index_sequence<sizeof...(Ts)>;
+
+// Tag types
+
+#ifdef ABSL_HAVE_STD_OPTIONAL
+
+using std::in_place_t;
+using std::in_place;
+
+#else  // ABSL_HAVE_STD_OPTIONAL
+
+// Tag type used in order to specify in-place construction, such as with
+// absl::optional.
+struct in_place_t {};
+extern const in_place_t in_place;
+
+#endif  // ABSL_HAVE_STD_OPTIONAL
+
+#ifdef ABSL_HAVE_STD_ANY
+using std::in_place_type_t;
+#else
+// Tag types used for in-place construction when the type to construct needs to
+// be specified, such as with absl::variant and absl::any.
+template <typename T>
+struct in_place_type_t {};
+#endif  // ABSL_HAVE_STD_ANY
+
+template <size_t I>
+struct in_place_index_t {};
+
+// Constexpr move and forward
+
+template <typename T>
+constexpr absl::remove_reference_t<T>&& move(T&& t) noexcept {
+  return static_cast<absl::remove_reference_t<T>&&>(t);
+}
+
+template <typename T>
+constexpr T&& forward(
+    absl::remove_reference_t<T>& t) noexcept {  // NOLINT(runtime/references)
+  return static_cast<T&&>(t);
+}
+
+}  // namespace absl
+
+#endif  // ABSL_UTILITY_UTILITY_H_
diff --git a/absl/utility/utility_test.cc b/absl/utility/utility_test.cc
new file mode 100644
index 000000000000..62cb46f4d160
--- /dev/null
+++ b/absl/utility/utility_test.cc
@@ -0,0 +1,163 @@
+// Copyright 2017 The Abseil Authors.
+//
+// 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 "absl/utility/utility.h"
+
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/attributes.h"
+
+namespace {
+
+#ifdef _MSC_VER
+// Warnings for unused variables in this test are false positives.  On other
+// platforms, they are suppressed by ABSL_ATTRIBUTE_UNUSED, but that doesn't
+// work on MSVC.
+// Both the unused variables and the name length warnings are due to calls
+// to absl::make_index_sequence with very large values, creating very long type
+// names. The resulting warnings are so long they make build output unreadable.
+#pragma warning( push )
+#pragma warning( disable : 4503 )  // decorated name length exceeded
+#pragma warning( disable : 4101 )  // unreferenced local variable
+#endif  // _MSC_VER
+
+using testing::StaticAssertTypeEq;
+using testing::ElementsAre;
+
+TEST(IntegerSequenceTest, ValueType) {
+  StaticAssertTypeEq<int, absl::integer_sequence<int>::value_type>();
+  StaticAssertTypeEq<char, absl::integer_sequence<char>::value_type>();
+}
+
+TEST(IntegerSequenceTest, Size) {
+  EXPECT_EQ(0, (absl::integer_sequence<int>::size()));
+  EXPECT_EQ(1, (absl::integer_sequence<int, 0>::size()));
+  EXPECT_EQ(1, (absl::integer_sequence<int, 1>::size()));
+  EXPECT_EQ(2, (absl::integer_sequence<int, 1, 2>::size()));
+  EXPECT_EQ(3, (absl::integer_sequence<int, 0, 1, 2>::size()));
+  EXPECT_EQ(3, (absl::integer_sequence<int, -123, 123, 456>::size()));
+  constexpr size_t sz = absl::integer_sequence<int, 0, 1>::size();
+  EXPECT_EQ(2, sz);
+}
+
+TEST(IntegerSequenceTest, MakeIndexSequence) {
+  StaticAssertTypeEq<absl::index_sequence<>, absl::make_index_sequence<0>>();
+  StaticAssertTypeEq<absl::index_sequence<0>, absl::make_index_sequence<1>>();
+  StaticAssertTypeEq<absl::index_sequence<0, 1>,
+                     absl::make_index_sequence<2>>();
+  StaticAssertTypeEq<absl::index_sequence<0, 1, 2>,
+                     absl::make_index_sequence<3>>();
+}
+
+TEST(IntegerSequenceTest, MakeIntegerSequence) {
+  StaticAssertTypeEq<absl::integer_sequence<int>,
+                     absl::make_integer_sequence<int, 0>>();
+  StaticAssertTypeEq<absl::integer_sequence<int, 0>,
+                     absl::make_integer_sequence<int, 1>>();
+  StaticAssertTypeEq<absl::integer_sequence<int, 0, 1>,
+                     absl::make_integer_sequence<int, 2>>();
+  StaticAssertTypeEq<absl::integer_sequence<int, 0, 1, 2>,
+                     absl::make_integer_sequence<int, 3>>();
+}
+
+template <typename... Ts>
+class Counter {};
+
+template <size_t... Is>
+void CountAll(absl::index_sequence<Is...>) {
+  // We only need an alias here, but instantiate a variable to silence warnings
+  // for unused typedefs in some compilers.
+  ABSL_ATTRIBUTE_UNUSED Counter<absl::make_index_sequence<Is>...> seq;
+}
+
+// This test verifies that absl::make_index_sequence can handle large arguments
+// without blowing up template instantiation stack, going OOM or taking forever
+// to compile (there is hard 15 minutes limit imposed by forge).
+TEST(IntegerSequenceTest, MakeIndexSequencePerformance) {
+  // O(log N) template instantiations.
+  // We only need an alias here, but instantiate a variable to silence warnings
+  // for unused typedefs in some compilers.
+  ABSL_ATTRIBUTE_UNUSED absl::make_index_sequence<(1 << 16) - 1> seq;
+  // O(N) template instantiations.
+  CountAll(absl::make_index_sequence<(1 << 8) - 1>());
+}
+
+template <typename F, typename Tup, size_t... Is>
+auto ApplyFromTupleImpl(F f, const Tup& tup, absl::index_sequence<Is...>)
+    -> decltype(f(std::get<Is>(tup)...)) {
+  return f(std::get<Is>(tup)...);
+}
+
+template <typename Tup>
+using TupIdxSeq = absl::make_index_sequence<std::tuple_size<Tup>::value>;
+
+template <typename F, typename Tup>
+auto ApplyFromTuple(F f, const Tup& tup)
+    -> decltype(ApplyFromTupleImpl(f, tup, TupIdxSeq<Tup>{})) {
+  return ApplyFromTupleImpl(f, tup, TupIdxSeq<Tup>{});
+}
+
+template <typename T>
+std::string Fmt(const T& x) {
+  std::ostringstream os;
+  os << x;
+  return os.str();
+}
+
+struct PoorStrCat {
+  template <typename... Args>
+  std::string operator()(const Args&... args) const {
+    std::string r;
+    for (const auto& e : {Fmt(args)...}) r += e;
+    return r;
+  }
+};
+
+template <typename Tup, size_t... Is>
+std::vector<std::string> TupStringVecImpl(const Tup& tup,
+                                     absl::index_sequence<Is...>) {
+  return {Fmt(std::get<Is>(tup))...};
+}
+
+template <typename... Ts>
+std::vector<std::string> TupStringVec(const std::tuple<Ts...>& tup) {
+  return TupStringVecImpl(tup, absl::index_sequence_for<Ts...>());
+}
+
+TEST(MakeIndexSequenceTest, ApplyFromTupleExample) {
+  PoorStrCat f{};
+  EXPECT_EQ("12abc3.14", f(12, "abc", 3.14));
+  EXPECT_EQ("12abc3.14", ApplyFromTuple(f, std::make_tuple(12, "abc", 3.14)));
+}
+
+TEST(IndexSequenceForTest, Basic) {
+  StaticAssertTypeEq<absl::index_sequence<>, absl::index_sequence_for<>>();
+  StaticAssertTypeEq<absl::index_sequence<0>, absl::index_sequence_for<int>>();
+  StaticAssertTypeEq<absl::index_sequence<0, 1, 2, 3>,
+                     absl::index_sequence_for<int, void, char, int>>();
+}
+
+TEST(IndexSequenceForTest, Example) {
+  EXPECT_THAT(TupStringVec(std::make_tuple(12, "abc", 3.14)),
+              ElementsAre("12", "abc", "3.14"));
+}
+
+}  // namespace
+