Creation of LTS branch "lts_2018_12_18"20181200

  - 44b0fafc62d9b8f192e8180cbe9c4b806b339d57 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 926bfeb9fff223429c12224b7514243886323e8d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 13327debebc5c2d1d4991b69fe50450e340e50e4 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 3088e76c597e068479e82508b1770a7ad0c806b6 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f6ae816808cd913e0e2b3e2af14f328fa1071af0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a06c4a1d9093137b7217a5aaba8920d62e835dc0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 7b46e1d31a6b08b1c6da2a13e7b151a20446fa07 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 070f6e47b33a2909d039e620c873204f78809492 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 7990fd459e9339467814ddb95000c87cb1e4d945 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f95179062eb65ce40895cc76f1398cce25394369 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - cc8dcd307b76a575d2e3e0958a4fe4c7193c2f68 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a705aa78dc76fc5c79d501e61dcc077eca68a8a4 Merge pull request #194 from Mizux/windows by Xiaoyi Zhang <zhangxy988@gmail.com>
  - a4c3ffff11eec0ee45742f915c255e9f870b7e0f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 01174578651b73021d9b8c3820f6fea707dacdf0 Merge pull request #201 from ccawley2011/fix-byteswap by Matt Calabrese <38107210+mattcalabrese-google@users.noreply.github.com>
  - f86f9413856b65afdd61fea938d684b8ab73115a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 94c298e2a0ae409e283cab96c954a685bd865a70 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 0884a6a04e4497d11b1b398cc0e422b118bf977a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - c16d5557cd05119b5b7b1318ef778ebe3195b4a1 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 45221ccc4ed643e4209b0cc5798e97203f108fa8 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 2019e17a520575ab365b2b5134d71068182c70b8 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5b70a8910b2e6fb0ce5193a41873139a126d2f7f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a00bdd176d66ef0b417d9576052a19091fbdf891 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f340f773edab951656b19b6f1a77c964a78ec4c2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 445998d7ac4e5d3c50411d377e3b50e960d2d6c2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - e821380d69a549dc64900693942789d21aa4df5e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f21d187b80e3b7f08fb279775ea9c8b48c636030 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5441bbe1db5d0f2ca24b5b60166367b0966790af Fix code snippet in comment (#174) by Loo Rong Jie <loorongjie@gmail.com>
  - 5aae0cffae8ffaacab965756169b34e511b353df Fix CMake build (#173) by Stephan Dollberg <stephan.dollberg@gmail.com>
  - 48cd2c3f351ff188bc85684b84a91b6e6d17d896 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - e291c279e458761e77a69b09b129d3d1e81f1e80 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - e01d95528ea2137a4a27a88d1f57c6cb260aafed Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 8ff1374008259719b54a8cb128ef951c02da164c Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 02451914b9ad5320f81f56a89f3eef1f8683227c Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 921fd5cf02ec0d665439a790148d59faa7d4a72c Merge pull request #166 from rongjiecomputer/cmake-test by Gennadiy Civil <gennadiycivil@users.noreply.github.com>
  - fb462224c058487763f263b7995d70efd0242c17 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - c075ad321696fa5072e097f0a51e4fe76a6fe13e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 0f4bc966754ec6cd28d5f03467d56f1efdc598e3 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 6c7e5ffc43decd92f7bdfc510ad8a245a20b6dea Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - d6df769173bf0263489f98874b93034db0e479a2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 28080f5f050c9530aa9f2b39c60d8217038d64ff Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 9c987f429bba32fb4446280fd3b91e2472d71d4d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5e7d459eeca7bc53deab0ee9634601386b53d7c0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - bed5bd6e185c7e0311f3a1f2dab4c96083dac636 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - fefc83638fb69395d259ed245699310610429064 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - d8cfe9f2a77fbee02c09642491e62a3f3677e0f6 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - ad5c960b2eb914881d1ceba0e996a0a8f3f6ca59 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 86f0fe93ad9d6d033a319476736a3256369c1f75 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f0f15c2778b0e4959244dd25e63f445a455870f5 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 29ff6d4860070bf8fcbd39c8805d0c32d56628a3 Removed "warning treated as error" flag from MSVC (#153) by vocaviking <vocaviking@users.noreply.github.com>
  - 083d04dd4a62ebbf037079b06e49b323c5e1192a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - bea85b52733022294eef108a2e42d77b616ddca2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 8f96be6ca60d967bd4b37f93d0a03bcff4145200 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 92e07e5590752d6b8e67f7f2f86c6286561e8cea Merge pull request #152 from clnperez/fix-multi-defines-p... by Derek Mauro <761129+derekmauro@users.noreply.github.com>
  - 2125e6444a9de9e41f21ecdc674dd7d8759c149d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 9acad869d21731f5bc50430a33fe61cc0ffcbb0b Merge pull request #150 from OlafvdSpek/patch-2 by Jonathan Cohen <cohenjon@google.com>
  - c2e00d341913bf03b4597ade5b056042e23e8c58 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 9e060686d1c325f34f9806b45fe77bafeed00aee Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 7aa411ceafc1272a28579cca739a97a2fb79055a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 2c5af55ed34850d8b7dd46177c8ca53fdfda920e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 44aa275286baf97fc13529aca547a88b180beb08 Merge pull request #143 from rongjiecomputer/kernel by Xiaoyi Zhang <zhangxy988@gmail.com>
  - 42f22a28401c952f1fc5942231c7fdac80811bf5 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - b973bc53ef366f0253b85eeed9a79b241884a843 Merge pull request #139 from siepkes/smartos-support by ahedberg <ahedberg@google.com>
  - e0def7473e52336f58759e11db4cd9467e5e0356 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f826f1d489b61b64df1d94afbe5981841a82e5fa Merge pull request #138 from edbaunton/remove-deprecated-... by ahedberg <ahedberg@google.com>
  - 7b50a4a94b0c7df68b3a854c850b551aaef0a8b4 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a5030ca5125b9d557ecfeea8acc8b1a8e49f6d27 Merge pull request #144 from rongjiecomputer/winsock2 by Xiaoyi Zhang <zhangxy988@gmail.com>
  - 02687955b7ca8fc02ada9b14bc247deeb108d341 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 8f612ebb152fb7e05643a2bcf78cb89a8c0641ad Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 134496a31d8b324f762de3bee9a002658c984456 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - ba8d6cf07766263723e86736f20a51c1c9c67b19 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - be1e84b988fceabcea4fc9e93f899539f0c81901 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 16ac2ec2e38cdf47f9330a312e319d57da659c10 Merge pull request #134 from rongjiecomputer/cmake by Alex Strelnikov <strel@google.com>
  - 7efd8dc0f1075356e9c7caa950afd1ecf854e8b9 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 87a4c07856e7dc69958019d47b2f02ae47746ec0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 4491d606df34c44efda47b6d17b605262f17e182 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>

GitOrigin-RevId: 44b0fafc62d9b8f192e8180cbe9c4b806b339d57
Change-Id: I2c427b5b41b2d34101922048b00f3d9dafcb498d

1 files changed, 740 insertions, 0 deletions

diff --git a/absl/container/internal/layout.h b/absl/container/internal/layout.h
new file mode 100644
index 00000000..f11a6ad2
--- /dev/null
+++ b/absl/container/internal/layout.h
@@ -0,0 +1,740 @@
+// Copyright 2018 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.
+//
+//                           MOTIVATION AND TUTORIAL
+//
+// If you want to put in a single heap allocation N doubles followed by M ints,
+// it's easy if N and M are known at compile time.
+//
+//   struct S {
+//     double a[N];
+//     int b[M];
+//   };
+//
+//   S* p = new S;
+//
+// But what if N and M are known only in run time? Class template Layout to the
+// rescue! It's a portable generalization of the technique known as struct hack.
+//
+//   // This object will tell us everything we need to know about the memory
+//   // layout of double[N] followed by int[M]. It's structurally identical to
+//   // size_t[2] that stores N and M. It's very cheap to create.
+//   const Layout<double, int> layout(N, M);
+//
+//   // Allocate enough memory for both arrays. `AllocSize()` tells us how much
+//   // memory is needed. We are free to use any allocation function we want as
+//   // long as it returns aligned memory.
+//   std::unique_ptr<unsigned char[]> p(new unsigned char[layout.AllocSize()]);
+//
+//   // Obtain the pointer to the array of doubles.
+//   // Equivalent to `reinterpret_cast<double*>(p.get())`.
+//   //
+//   // We could have written layout.Pointer<0>(p) instead. If all the types are
+//   // unique you can use either form, but if some types are repeated you must
+//   // use the index form.
+//   double* a = layout.Pointer<double>(p.get());
+//
+//   // Obtain the pointer to the array of ints.
+//   // Equivalent to `reinterpret_cast<int*>(p.get() + N * 8)`.
+//   int* b = layout.Pointer<int>(p);
+//
+// If we are unable to specify sizes of all fields, we can pass as many sizes as
+// we can to `Partial()`. In return, it'll allow us to access the fields whose
+// locations and sizes can be computed from the provided information.
+// `Partial()` comes in handy when the array sizes are embedded into the
+// allocation.
+//
+//   // size_t[1] containing N, size_t[1] containing M, double[N], int[M].
+//   using L = Layout<size_t, size_t, double, int>;
+//
+//   unsigned char* Allocate(size_t n, size_t m) {
+//     const L layout(1, 1, n, m);
+//     unsigned char* p = new unsigned char[layout.AllocSize()];
+//     *layout.Pointer<0>(p) = n;
+//     *layout.Pointer<1>(p) = m;
+//     return p;
+//   }
+//
+//   void Use(unsigned char* p) {
+//     // First, extract N and M.
+//     // Specify that the first array has only one element. Using `prefix` we
+//     // can access the first two arrays but not more.
+//     constexpr auto prefix = L::Partial(1);
+//     size_t n = *prefix.Pointer<0>(p);
+//     size_t m = *prefix.Pointer<1>(p);
+//
+//     // Now we can get pointers to the payload.
+//     const L layout(1, 1, n, m);
+//     double* a = layout.Pointer<double>(p);
+//     int* b = layout.Pointer<int>(p);
+//   }
+//
+// The layout we used above combines fixed-size with dynamically-sized fields.
+// This is quite common. Layout is optimized for this use case and generates
+// optimal code. All computations that can be performed at compile time are
+// indeed performed at compile time.
+//
+// Efficiency tip: The order of fields matters. In `Layout<T1, ..., TN>` try to
+// ensure that `alignof(T1) >= ... >= alignof(TN)`. This way you'll have no
+// padding in between arrays.
+//
+// You can manually override the alignment of an array by wrapping the type in
+// `Aligned<T, N>`. `Layout<..., Aligned<T, N>, ...>` has exactly the same API
+// and behavior as `Layout<..., T, ...>` except that the first element of the
+// array of `T` is aligned to `N` (the rest of the elements follow without
+// padding). `N` cannot be less than `alignof(T)`.
+//
+// `AllocSize()` and `Pointer()` are the most basic methods for dealing with
+// memory layouts. Check out the reference or code below to discover more.
+//
+//                            EXAMPLE
+//
+//   // Immutable move-only string with sizeof equal to sizeof(void*). The
+//   // string size and the characters are kept in the same heap allocation.
+//   class CompactString {
+//    public:
+//     CompactString(const char* s = "") {
+//       const size_t size = strlen(s);
+//       // size_t[1] followed by char[size + 1].
+//       const L layout(1, size + 1);
+//       p_.reset(new unsigned char[layout.AllocSize()]);
+//       // If running under ASAN, mark the padding bytes, if any, to catch
+//       // memory errors.
+//       layout.PoisonPadding(p_.get());
+//       // Store the size in the allocation.
+//       *layout.Pointer<size_t>(p_.get()) = size;
+//       // Store the characters in the allocation.
+//       memcpy(layout.Pointer<char>(p_.get()), s, size + 1);
+//     }
+//
+//     size_t size() const {
+//       // Equivalent to reinterpret_cast<size_t&>(*p).
+//       return *L::Partial().Pointer<size_t>(p_.get());
+//     }
+//
+//     const char* c_str() const {
+//       // Equivalent to reinterpret_cast<char*>(p.get() + sizeof(size_t)).
+//       // The argument in Partial(1) specifies that we have size_t[1] in front
+//       // of the characters.
+//       return L::Partial(1).Pointer<char>(p_.get());
+//     }
+//
+//    private:
+//     // Our heap allocation contains a size_t followed by an array of chars.
+//     using L = Layout<size_t, char>;
+//     std::unique_ptr<unsigned char[]> p_;
+//   };
+//
+//   int main() {
+//     CompactString s = "hello";
+//     assert(s.size() == 5);
+//     assert(strcmp(s.c_str(), "hello") == 0);
+//   }
+//
+//                               DOCUMENTATION
+//
+// The interface exported by this file consists of:
+// - class `Layout<>` and its public members.
+// - The public members of class `internal_layout::LayoutImpl<>`. That class
+//   isn't intended to be used directly, and its name and template parameter
+//   list are internal implementation details, but the class itself provides
+//   most of the functionality in this file. See comments on its members for
+//   detailed documentation.
+//
+// `Layout<T1,... Tn>::Partial(count1,..., countm)` (where `m` <= `n`) returns a
+// `LayoutImpl<>` object. `Layout<T1,..., Tn> layout(count1,..., countn)`
+// creates a `Layout` object, which exposes the same functionality by inheriting
+// from `LayoutImpl<>`.
+
+#ifndef ABSL_CONTAINER_INTERNAL_LAYOUT_H_
+#define ABSL_CONTAINER_INTERNAL_LAYOUT_H_
+
+#include <assert.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <ostream>
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <typeinfo>
+#include <utility>
+
+#ifdef ADDRESS_SANITIZER
+#include <sanitizer/asan_interface.h>
+#endif
+
+#include "absl/meta/type_traits.h"
+#include "absl/strings/str_cat.h"
+#include "absl/types/span.h"
+#include "absl/utility/utility.h"
+
+#if defined(__GXX_RTTI)
+#define ABSL_INTERNAL_HAS_CXA_DEMANGLE
+#endif
+
+#ifdef ABSL_INTERNAL_HAS_CXA_DEMANGLE
+#include <cxxabi.h>
+#endif
+
+namespace absl {
+inline namespace lts_2018_12_18 {
+namespace container_internal {
+
+// A type wrapper that instructs `Layout` to use the specific alignment for the
+// array. `Layout<..., Aligned<T, N>, ...>` has exactly the same API
+// and behavior as `Layout<..., T, ...>` except that the first element of the
+// array of `T` is aligned to `N` (the rest of the elements follow without
+// padding).
+//
+// Requires: `N >= alignof(T)` and `N` is a power of 2.
+template <class T, size_t N>
+struct Aligned;
+
+namespace internal_layout {
+
+template <class T>
+struct NotAligned {};
+
+template <class T, size_t N>
+struct NotAligned<const Aligned<T, N>> {
+  static_assert(sizeof(T) == 0, "Aligned<T, N> cannot be const-qualified");
+};
+
+template <size_t>
+using IntToSize = size_t;
+
+template <class>
+using TypeToSize = size_t;
+
+template <class T>
+struct Type : NotAligned<T> {
+  using type = T;
+};
+
+template <class T, size_t N>
+struct Type<Aligned<T, N>> {
+  using type = T;
+};
+
+template <class T>
+struct SizeOf : NotAligned<T>, std::integral_constant<size_t, sizeof(T)> {};
+
+template <class T, size_t N>
+struct SizeOf<Aligned<T, N>> : std::integral_constant<size_t, sizeof(T)> {};
+
+// Note: workaround for https://gcc.gnu.org/PR88115
+template <class T>
+struct AlignOf : NotAligned<T> {
+  static constexpr size_t value = alignof(T);
+};
+
+template <class T, size_t N>
+struct AlignOf<Aligned<T, N>> {
+  static_assert(N % alignof(T) == 0,
+                "Custom alignment can't be lower than the type's alignment");
+  static constexpr size_t value = N;
+};
+
+// Does `Ts...` contain `T`?
+template <class T, class... Ts>
+using Contains = absl::disjunction<std::is_same<T, Ts>...>;
+
+template <class From, class To>
+using CopyConst =
+    typename std::conditional<std::is_const<From>::value, const To, To>::type;
+
+// Note: We're not qualifying this with absl:: because it doesn't compile under
+// MSVC.
+template <class T>
+using SliceType = Span<T>;
+
+// This namespace contains no types. It prevents functions defined in it from
+// being found by ADL.
+namespace adl_barrier {
+
+template <class Needle, class... Ts>
+constexpr size_t Find(Needle, Needle, Ts...) {
+  static_assert(!Contains<Needle, Ts...>(), "Duplicate element type");
+  return 0;
+}
+
+template <class Needle, class T, class... Ts>
+constexpr size_t Find(Needle, T, Ts...) {
+  return adl_barrier::Find(Needle(), Ts()...) + 1;
+}
+
+constexpr bool IsPow2(size_t n) { return !(n & (n - 1)); }
+
+// Returns `q * m` for the smallest `q` such that `q * m >= n`.
+// Requires: `m` is a power of two. It's enforced by IsLegalElementType below.
+constexpr size_t Align(size_t n, size_t m) { return (n + m - 1) & ~(m - 1); }
+
+constexpr size_t Min(size_t a, size_t b) { return b < a ? b : a; }
+
+constexpr size_t Max(size_t a) { return a; }
+
+template <class... Ts>
+constexpr size_t Max(size_t a, size_t b, Ts... rest) {
+  return adl_barrier::Max(b < a ? a : b, rest...);
+}
+
+template <class T>
+std::string TypeName() {
+  std::string out;
+  int status = 0;
+  char* demangled = nullptr;
+#ifdef ABSL_INTERNAL_HAS_CXA_DEMANGLE
+  demangled = abi::__cxa_demangle(typeid(T).name(), nullptr, nullptr, &status);
+#endif
+  if (status == 0 && demangled != nullptr) {  // Demangling succeeded.
+    absl::StrAppend(&out, "<", demangled, ">");
+    free(demangled);
+  } else {
+#if defined(__GXX_RTTI) || defined(_CPPRTTI)
+    absl::StrAppend(&out, "<", typeid(T).name(), ">");
+#endif
+  }
+  return out;
+}
+
+}  // namespace adl_barrier
+
+template <bool C>
+using EnableIf = typename std::enable_if<C, int>::type;
+
+// Can `T` be a template argument of `Layout`?
+template <class T>
+using IsLegalElementType = std::integral_constant<
+    bool, !std::is_reference<T>::value && !std::is_volatile<T>::value &&
+              !std::is_reference<typename Type<T>::type>::value &&
+              !std::is_volatile<typename Type<T>::type>::value &&
+              adl_barrier::IsPow2(AlignOf<T>::value)>;
+
+template <class Elements, class SizeSeq, class OffsetSeq>
+class LayoutImpl;
+
+// Public base class of `Layout` and the result type of `Layout::Partial()`.
+//
+// `Elements...` contains all template arguments of `Layout` that created this
+// instance.
+//
+// `SizeSeq...` is `[0, NumSizes)` where `NumSizes` is the number of arguments
+// passed to `Layout::Partial()` or `Layout::Layout()`.
+//
+// `OffsetSeq...` is `[0, NumOffsets)` where `NumOffsets` is
+// `Min(sizeof...(Elements), NumSizes + 1)` (the number of arrays for which we
+// can compute offsets).
+template <class... Elements, size_t... SizeSeq, size_t... OffsetSeq>
+class LayoutImpl<std::tuple<Elements...>, absl::index_sequence<SizeSeq...>,
+                 absl::index_sequence<OffsetSeq...>> {
+ private:
+  static_assert(sizeof...(Elements) > 0, "At least one field is required");
+  static_assert(absl::conjunction<IsLegalElementType<Elements>...>::value,
+                "Invalid element type (see IsLegalElementType)");
+
+  enum {
+    NumTypes = sizeof...(Elements),
+    NumSizes = sizeof...(SizeSeq),
+    NumOffsets = sizeof...(OffsetSeq),
+  };
+
+  // These are guaranteed by `Layout`.
+  static_assert(NumOffsets == adl_barrier::Min(NumTypes, NumSizes + 1),
+                "Internal error");
+  static_assert(NumTypes > 0, "Internal error");
+
+  // Returns the index of `T` in `Elements...`. Results in a compilation error
+  // if `Elements...` doesn't contain exactly one instance of `T`.
+  template <class T>
+  static constexpr size_t ElementIndex() {
+    static_assert(Contains<Type<T>, Type<typename Type<Elements>::type>...>(),
+                  "Type not found");
+    return adl_barrier::Find(Type<T>(),
+                             Type<typename Type<Elements>::type>()...);
+  }
+
+  template <size_t N>
+  using ElementAlignment =
+      AlignOf<typename std::tuple_element<N, std::tuple<Elements...>>::type>;
+
+ public:
+  // Element types of all arrays packed in a tuple.
+  using ElementTypes = std::tuple<typename Type<Elements>::type...>;
+
+  // Element type of the Nth array.
+  template <size_t N>
+  using ElementType = typename std::tuple_element<N, ElementTypes>::type;
+
+  constexpr explicit LayoutImpl(IntToSize<SizeSeq>... sizes)
+      : size_{sizes...} {}
+
+  // Alignment of the layout, equal to the strictest alignment of all elements.
+  // All pointers passed to the methods of layout must be aligned to this value.
+  static constexpr size_t Alignment() {
+    return adl_barrier::Max(AlignOf<Elements>::value...);
+  }
+
+  // Offset in bytes of the Nth array.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   assert(x.Offset<0>() == 0);   // The ints starts from 0.
+  //   assert(x.Offset<1>() == 16);  // The doubles starts from 16.
+  //
+  // Requires: `N <= NumSizes && N < sizeof...(Ts)`.
+  template <size_t N, EnableIf<N == 0> = 0>
+  constexpr size_t Offset() const {
+    return 0;
+  }
+
+  template <size_t N, EnableIf<N != 0> = 0>
+  constexpr size_t Offset() const {
+    static_assert(N < NumOffsets, "Index out of bounds");
+    return adl_barrier::Align(
+        Offset<N - 1>() + SizeOf<ElementType<N - 1>>() * size_[N - 1],
+        ElementAlignment<N>::value);
+  }
+
+  // Offset in bytes of the array with the specified element type. There must
+  // be exactly one such array and its zero-based index must be at most
+  // `NumSizes`.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   assert(x.Offset<int>() == 0);      // The ints starts from 0.
+  //   assert(x.Offset<double>() == 16);  // The doubles starts from 16.
+  template <class T>
+  constexpr size_t Offset() const {
+    return Offset<ElementIndex<T>()>();
+  }
+
+  // Offsets in bytes of all arrays for which the offsets are known.
+  constexpr std::array<size_t, NumOffsets> Offsets() const {
+    return {{Offset<OffsetSeq>()...}};
+  }
+
+  // The number of elements in the Nth array. This is the Nth argument of
+  // `Layout::Partial()` or `Layout::Layout()` (zero-based).
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   assert(x.Size<0>() == 3);
+  //   assert(x.Size<1>() == 4);
+  //
+  // Requires: `N < NumSizes`.
+  template <size_t N>
+  constexpr size_t Size() const {
+    static_assert(N < NumSizes, "Index out of bounds");
+    return size_[N];
+  }
+
+  // The number of elements in the array with the specified element type.
+  // There must be exactly one such array and its zero-based index must be
+  // at most `NumSizes`.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   assert(x.Size<int>() == 3);
+  //   assert(x.Size<double>() == 4);
+  template <class T>
+  constexpr size_t Size() const {
+    return Size<ElementIndex<T>()>();
+  }
+
+  // The number of elements of all arrays for which they are known.
+  constexpr std::array<size_t, NumSizes> Sizes() const {
+    return {{Size<SizeSeq>()...}};
+  }
+
+  // Pointer to the beginning of the Nth array.
+  //
+  // `Char` must be `[const] [signed|unsigned] char`.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   unsigned char* p = new unsigned char[x.AllocSize()];
+  //   int* ints = x.Pointer<0>(p);
+  //   double* doubles = x.Pointer<1>(p);
+  //
+  // Requires: `N <= NumSizes && N < sizeof...(Ts)`.
+  // Requires: `p` is aligned to `Alignment()`.
+  template <size_t N, class Char>
+  CopyConst<Char, ElementType<N>>* Pointer(Char* p) const {
+    using C = typename std::remove_const<Char>::type;
+    static_assert(
+        std::is_same<C, char>() || std::is_same<C, unsigned char>() ||
+            std::is_same<C, signed char>(),
+        "The argument must be a pointer to [const] [signed|unsigned] char");
+    constexpr size_t alignment = Alignment();
+    (void)alignment;
+    assert(reinterpret_cast<uintptr_t>(p) % alignment == 0);
+    return reinterpret_cast<CopyConst<Char, ElementType<N>>*>(p + Offset<N>());
+  }
+
+  // Pointer to the beginning of the array with the specified element type.
+  // There must be exactly one such array and its zero-based index must be at
+  // most `NumSizes`.
+  //
+  // `Char` must be `[const] [signed|unsigned] char`.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   unsigned char* p = new unsigned char[x.AllocSize()];
+  //   int* ints = x.Pointer<int>(p);
+  //   double* doubles = x.Pointer<double>(p);
+  //
+  // Requires: `p` is aligned to `Alignment()`.
+  template <class T, class Char>
+  CopyConst<Char, T>* Pointer(Char* p) const {
+    return Pointer<ElementIndex<T>()>(p);
+  }
+
+  // Pointers to all arrays for which pointers are known.
+  //
+  // `Char` must be `[const] [signed|unsigned] char`.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   unsigned char* p = new unsigned char[x.AllocSize()];
+  //
+  //   int* ints;
+  //   double* doubles;
+  //   std::tie(ints, doubles) = x.Pointers(p);
+  //
+  // Requires: `p` is aligned to `Alignment()`.
+  //
+  // Note: We're not using ElementType alias here because it does not compile
+  // under MSVC.
+  template <class Char>
+  std::tuple<CopyConst<
+      Char, typename std::tuple_element<OffsetSeq, ElementTypes>::type>*...>
+  Pointers(Char* p) const {
+    return std::tuple<CopyConst<Char, ElementType<OffsetSeq>>*...>(
+        Pointer<OffsetSeq>(p)...);
+  }
+
+  // The Nth array.
+  //
+  // `Char` must be `[const] [signed|unsigned] char`.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   unsigned char* p = new unsigned char[x.AllocSize()];
+  //   Span<int> ints = x.Slice<0>(p);
+  //   Span<double> doubles = x.Slice<1>(p);
+  //
+  // Requires: `N < NumSizes`.
+  // Requires: `p` is aligned to `Alignment()`.
+  template <size_t N, class Char>
+  SliceType<CopyConst<Char, ElementType<N>>> Slice(Char* p) const {
+    return SliceType<CopyConst<Char, ElementType<N>>>(Pointer<N>(p), Size<N>());
+  }
+
+  // The array with the specified element type. There must be exactly one
+  // such array and its zero-based index must be less than `NumSizes`.
+  //
+  // `Char` must be `[const] [signed|unsigned] char`.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   unsigned char* p = new unsigned char[x.AllocSize()];
+  //   Span<int> ints = x.Slice<int>(p);
+  //   Span<double> doubles = x.Slice<double>(p);
+  //
+  // Requires: `p` is aligned to `Alignment()`.
+  template <class T, class Char>
+  SliceType<CopyConst<Char, T>> Slice(Char* p) const {
+    return Slice<ElementIndex<T>()>(p);
+  }
+
+  // All arrays with known sizes.
+  //
+  // `Char` must be `[const] [signed|unsigned] char`.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   unsigned char* p = new unsigned char[x.AllocSize()];
+  //
+  //   Span<int> ints;
+  //   Span<double> doubles;
+  //   std::tie(ints, doubles) = x.Slices(p);
+  //
+  // Requires: `p` is aligned to `Alignment()`.
+  //
+  // Note: We're not using ElementType alias here because it does not compile
+  // under MSVC.
+  template <class Char>
+  std::tuple<SliceType<CopyConst<
+      Char, typename std::tuple_element<SizeSeq, ElementTypes>::type>>...>
+  Slices(Char* p) const {
+    // Workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63875 (fixed
+    // in 6.1).
+    (void)p;
+    return std::tuple<SliceType<CopyConst<Char, ElementType<SizeSeq>>>...>(
+        Slice<SizeSeq>(p)...);
+  }
+
+  // The size of the allocation that fits all arrays.
+  //
+  //   // int[3], 4 bytes of padding, double[4].
+  //   Layout<int, double> x(3, 4);
+  //   unsigned char* p = new unsigned char[x.AllocSize()];  // 48 bytes
+  //
+  // Requires: `NumSizes == sizeof...(Ts)`.
+  constexpr size_t AllocSize() const {
+    static_assert(NumTypes == NumSizes, "You must specify sizes of all fields");
+    return Offset<NumTypes - 1>() +
+           SizeOf<ElementType<NumTypes - 1>>() * size_[NumTypes - 1];
+  }
+
+  // If built with --config=asan, poisons padding bytes (if any) in the
+  // allocation. The pointer must point to a memory block at least
+  // `AllocSize()` bytes in length.
+  //
+  // `Char` must be `[const] [signed|unsigned] char`.
+  //
+  // Requires: `p` is aligned to `Alignment()`.
+  template <class Char, size_t N = NumOffsets - 1, EnableIf<N == 0> = 0>
+  void PoisonPadding(const Char* p) const {
+    Pointer<0>(p);  // verify the requirements on `Char` and `p`
+  }
+
+  template <class Char, size_t N = NumOffsets - 1, EnableIf<N != 0> = 0>
+  void PoisonPadding(const Char* p) const {
+    static_assert(N < NumOffsets, "Index out of bounds");
+    (void)p;
+#ifdef ADDRESS_SANITIZER
+    PoisonPadding<Char, N - 1>(p);
+    // The `if` is an optimization. It doesn't affect the observable behaviour.
+    if (ElementAlignment<N - 1>::value % ElementAlignment<N>::value) {
+      size_t start =
+          Offset<N - 1>() + SizeOf<ElementType<N - 1>>() * size_[N - 1];
+      ASAN_POISON_MEMORY_REGION(p + start, Offset<N>() - start);
+    }
+#endif
+  }
+
+  // Human-readable description of the memory layout. Useful for debugging.
+  // Slow.
+  //
+  //   // char[5], 3 bytes of padding, int[3], 4 bytes of padding, followed
+  //   // by an unknown number of doubles.
+  //   auto x = Layout<char, int, double>::Partial(5, 3);
+  //   assert(x.DebugString() ==
+  //          "@0<char>(1)[5]; @8<int>(4)[3]; @24<double>(8)");
+  //
+  // Each field is in the following format: @offset<type>(sizeof)[size] (<type>
+  // may be missing depending on the target platform). For example,
+  // @8<int>(4)[3] means that at offset 8 we have an array of ints, where each
+  // int is 4 bytes, and we have 3 of those ints. The size of the last field may
+  // be missing (as in the example above). Only fields with known offsets are
+  // described. Type names may differ across platforms: one compiler might
+  // produce "unsigned*" where another produces "unsigned int *".
+  std::string DebugString() const {
+    const auto offsets = Offsets();
+    const size_t sizes[] = {SizeOf<ElementType<OffsetSeq>>()...};
+    const std::string types[] = {adl_barrier::TypeName<ElementType<OffsetSeq>>()...};
+    std::string res = absl::StrCat("@0", types[0], "(", sizes[0], ")");
+    for (size_t i = 0; i != NumOffsets - 1; ++i) {
+      absl::StrAppend(&res, "[", size_[i], "]; @", offsets[i + 1], types[i + 1],
+                      "(", sizes[i + 1], ")");
+    }
+    // NumSizes is a constant that may be zero. Some compilers cannot see that
+    // inside the if statement "size_[NumSizes - 1]" must be valid.
+    int last = static_cast<int>(NumSizes) - 1;
+    if (NumTypes == NumSizes && last >= 0) {
+      absl::StrAppend(&res, "[", size_[last], "]");
+    }
+    return res;
+  }
+
+ private:
+  // Arguments of `Layout::Partial()` or `Layout::Layout()`.
+  size_t size_[NumSizes > 0 ? NumSizes : 1];
+};
+
+template <size_t NumSizes, class... Ts>
+using LayoutType = LayoutImpl<
+    std::tuple<Ts...>, absl::make_index_sequence<NumSizes>,
+    absl::make_index_sequence<adl_barrier::Min(sizeof...(Ts), NumSizes + 1)>>;
+
+}  // namespace internal_layout
+
+// Descriptor of arrays of various types and sizes laid out in memory one after
+// another. See the top of the file for documentation.
+//
+// Check out the public API of internal_layout::LayoutImpl above. The type is
+// internal to the library but its methods are public, and they are inherited
+// by `Layout`.
+template <class... Ts>
+class Layout : public internal_layout::LayoutType<sizeof...(Ts), Ts...> {
+ public:
+  static_assert(sizeof...(Ts) > 0, "At least one field is required");
+  static_assert(
+      absl::conjunction<internal_layout::IsLegalElementType<Ts>...>::value,
+      "Invalid element type (see IsLegalElementType)");
+
+  // The result type of `Partial()` with `NumSizes` arguments.
+  template <size_t NumSizes>
+  using PartialType = internal_layout::LayoutType<NumSizes, Ts...>;
+
+  // `Layout` knows the element types of the arrays we want to lay out in
+  // memory but not the number of elements in each array.
+  // `Partial(size1, ..., sizeN)` allows us to specify the latter. The
+  // resulting immutable object can be used to obtain pointers to the
+  // individual arrays.
+  //
+  // It's allowed to pass fewer array sizes than the number of arrays. E.g.,
+  // if all you need is to the offset of the second array, you only need to
+  // pass one argument -- the number of elements in the first array.
+  //
+  //   // int[3] followed by 4 bytes of padding and an unknown number of
+  //   // doubles.
+  //   auto x = Layout<int, double>::Partial(3);
+  //   // doubles start at byte 16.
+  //   assert(x.Offset<1>() == 16);
+  //
+  // If you know the number of elements in all arrays, you can still call
+  // `Partial()` but it's more convenient to use the constructor of `Layout`.
+  //
+  //   Layout<int, double> x(3, 5);
+  //
+  // Note: The sizes of the arrays must be specified in number of elements,
+  // not in bytes.
+  //
+  // Requires: `sizeof...(Sizes) <= sizeof...(Ts)`.
+  // Requires: all arguments are convertible to `size_t`.
+  template <class... Sizes>
+  static constexpr PartialType<sizeof...(Sizes)> Partial(Sizes&&... sizes) {
+    static_assert(sizeof...(Sizes) <= sizeof...(Ts), "");
+    return PartialType<sizeof...(Sizes)>(absl::forward<Sizes>(sizes)...);
+  }
+
+  // Creates a layout with the sizes of all arrays specified. If you know
+  // only the sizes of the first N arrays (where N can be zero), you can use
+  // `Partial()` defined above. The constructor is essentially equivalent to
+  // calling `Partial()` and passing in all array sizes; the constructor is
+  // provided as a convenient abbreviation.
+  //
+  // Note: The sizes of the arrays must be specified in number of elements,
+  // not in bytes.
+  constexpr explicit Layout(internal_layout::TypeToSize<Ts>... sizes)
+      : internal_layout::LayoutType<sizeof...(Ts), Ts...>(sizes...) {}
+};
+
+}  // namespace container_internal
+}  // inline namespace lts_2018_12_18
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_INTERNAL_LAYOUT_H_