Creation of LTS branch "lts_2019_08_08"

  - 9ee91d3e430fb33a4590486573792eb0fa146c2d Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 8efba58a3b656e9b41fb0471ae6453425a61c520 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - b49b8d16b67ec6912899684b732e6367f258cfdb Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 67222ffc4c83d918ce8395aa61769eeb77df4c4d Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - c5c4db4f5191fe5e76cbf68dcc71fb28702f7d2b Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 14550beb3b7b97195e483fb74b5efb906395c31e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 52e88ee56b72cf32bc66534d942c7398ce481331 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 36d37ab992038f52276ca66b9da80c1cf0f57dc2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - ad1485c8986246b2ae9105e512738d0e97aec887 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f3840bc5e33ce4932e35986cf3718450c6f02af2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 278b26058c036833a4f7f3047d3f4d9296527f87 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - c6c3c1b498e4ee939b24be59cae29d59c3863be8 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 44efe96dfca674a17b45ca53fc77fb69f1e29bf4 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 3c98fcc0461bd2a4b9c149d4748a7373a225cf4b Merge pull request #340 from jtsylve/macos_cxx17_fix by Matt Calabrese <38107210+mattcalabrese-google@users.noreply.github.com>
  - 74d91756c11bc22f9b0108b94da9326f7f9e376f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - e6b050212c859fbaf67abac76105da10ec348274 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - c964fcffac27bd4a9ff67fe393410dd1146ef8b8 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 72e09a54d993b192db32be14c65adf7e9bd08c31 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - d65e19dfcd8697076f68598c0131c6930cdcd74d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5162fc83d2f3b79a9753ed59594c43966afdd37a Merge pull request #336 from shields/patch-2 by Shaindel Schwartz <31392632+shaindelschwartz@users.noreply.github.com>
  - 0389f7bf58fa41f35b3ad60be61d32f31e4f8ed6 Merge pull request #335 from shields/patch-1 by Shaindel Schwartz <31392632+shaindelschwartz@users.noreply.github.com>
  - e9324d926a9189e222741fce6e676f0944661a72 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 43ef2148c0936ebf7cb4be6b19927a9d9d145b8f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a13d3df2b3ba68aeead92e2d078fba0510d55024 Merge pull request #323 from gosnik/master by Gennadiy Rozental <rogeeff@google.com>
  - 310a11865c97c5cdcc42a4ee2c2e3578423afe69 Merge pull request #324 from RasPat1/patch-1 by Gennadiy Rozental <rogeeff@google.com>
  - 8f11724067248acc330b4d1f12f0c76d03f2cfb1 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - b1dd425423380126f6441ce4fbb6f8f6c75b793a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 361cb8a9db2f2130442389fd80593255be26d681 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 0238ab0a831f179518c1a814f9584e99da2d75a3 Merge pull request #321 from christoph-cullmann/c4245_fix... by Xiaoyi Zhang <zhangxy988@gmail.com>
  - 61c9bf3e3e1c28a4aa6d7f1be4b37fd473bb5529 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - bc9101f9982391019521161a36179b52555ed212 Merge pull request #320 from christoph-cullmann/master by Xiaoyi Zhang <zhangxy988@gmail.com>
  - 2f76a9bf50046e396138cc8eeb3cdc17b7a5ac24 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 4adaf5490921f13028b55018c9f550277de5aebb Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 27c30ec671cb7b5ba84c4e79feff7fd0b0ac6338 Avoid undefined behavior when nullptr is passed to memcpy... by Roman Gershman <romange@gmail.com>
  - ce65f5ac3cbf897bb5e3de1a51d80fd00866abaa Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a18fc7461e7409c2ad64e28537261db1e02e76fa Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 8a394b19c149cab50534b04c5e21d42bc2217a7d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - daf381e8535a1f1f1b8a75966a74e7cca63dee89 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - fa00c321073c7ea40a4fc3dfc8a06309eae3d025 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 436ba6c4a0ea3a06eca6e055f9c8d296bf3bae12 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 0cbdc774b97f7e80ab60dbe2ed4eaca3b2e33fc8 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 27c2f6e2f3b5929fbd322b0f0ca392eb02efd9f8 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - aa468ad75539619b47979911297efbb629c52e44 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - cd86d0d20ab167c33b23d3875db68d1d4bad3a3b Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 33841c5c963aa9c3f096ef8e6c1e71624b941940 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - ca3f87560a0eef716195cadf66dc6b938a579ec6 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - d902eb869bcfacc1bad14933ed9af4bed006d481 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a02f62f456f2c4a7ecf2be3104fe0c6e16fbad9a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 0b545b460141b882b244a1efcef7621d59278160 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - dbae8764fbd429bf7d7745e24bcf73962177a7c0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 044da8a29c923506af0f0b46bc46f43c1e1300b5 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 6cc6ac44e065b9e8975fadfd6ccb99cbcf89aac4 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 666fc1266bccfd8e6eaaa084e7b42580bb8eb199 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 93dfcf74cb5fccae3da07897d8613ae6cab958a0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 2c8421e1c6cef0da9e8a20b01c15256ec9ec116d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5b65c4af5107176555b23a638e5947686410ac1f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - eab2078b53c9e3d9d240135c09d27e3393acb50a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 253eb7416421661873afbaa33828a850db978541 [CMake] Set correct flags for clang-cl (#278) by Loo Rong Jie <loorongjie@gmail.com>
  - e75672f6afc7e8f23ee7b532e86d1b3b9be3984e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - bf29470384a101b307873b26d358433138c857fc Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 6fd827124facd8336981e73218997f9e73029b4f Merge pull request #280 from chiumichael/master by Derek Mauro <761129+derekmauro@users.noreply.github.com>
  - 7c7754fb3ed9ffb57d35fe8658f3ba4d73a31e72 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 256be563447a315f2a7993ec669460ba475fa86a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 88a152ae747c3c42dc9167d46c590929b048d436 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - c1cecb25a94c075725e9d2640f6b978a8f61957b Implement Span::first and Span::last from C++20 (#274) by Girts <girtsf@users.noreply.github.com>
  - 38b704384cd2f17590b3922b97744be0b43622c9 Changed HTTP URLs to HTTPS where possible (#270) by nik7273 <nik8470@gmail.com>
  - febc5ee6a92d0eb7dac1fceaa6c648cf6521b4dc Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 9fdf5e5b805412cb2a2e624d3e9a11588120465f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 419f3184f8ebcdb23105295eadd2a569f3351eb9 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - b312c3cb53a0aad75a85ac2bf57c4a614fbd48d4 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 308ce31528a7edfa39f5f6d36142278a0ae1bf45 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 93d155bc4414f6c121bb1f19dba9fdb27c8943bc Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 426eaa4aa44e4580418bee46c1bd13911151bfb1 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 2901ec32a919311384d6ad4194e2d927c06831f7 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - d78310fe5a82f2e0e6e16509ef8079c8d7e4674e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a4cb1c8ba61531a63f9d309eea01ac1d43d8371d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 540e2537b92cd4abfae6ceddfe24304345461f32 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 89ea0c5ff34aaa5855cfc7aa41f323b8a0ef0ede Merge pull request #255 from uilianries/hotfix/conan by ahedberg <ahedberg@google.com>
  - 5e0dcf72c64fae912184d2e0de87195fe8f0a425 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 0dffca4e36791c7beeda04da10460b534283948a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 6b4201f9ef650637510a21b8d6cbcc3bee4a606f Fix GCC8 warnings by Boris Staletic <boris.staletic@gmail.com>
  - 0b1e6d417b414aad9282e32e8c49c719edeb63c1 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - efccc502606bed768e50a6cd5806d8eb13e4e935 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5e6a78131f7bd5940218462c07d88cdefdd75dbe Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5eea0f713c14ac17788b83e496f11903f8e2bbb0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 66f9becbb98ecc083f4db349b4b1e0ca9de93b15 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 018b4db1d73ec8238e6dc4b17fd9e1fd7468d0ed Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 9449ae94397f2fd683851348e25ed8c93f75b3b9 Merge pull request #243 from ThomsonTan/FixIntrinsic by Alex Strelnikov <strel@google.com>
  - b16aeb6756bdab08cdf12d40baab5b51f7d15b16 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 7ffbe09f3d85504bd018783bbe1e2c12992fe47c Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 01b471d9f3ebef27f5aaca14b66509099fa8cd6c Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 7bd8f36c741c7cbe311611d7981bf38ba04c6fef Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 968a34ffdaadd7db062a9621dfbdf8b2d16e05af Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 3e2e9b5557e76d098de4b8a2a659125b98ca519b Merge pull request #231 from uilianries/feature/conan by Mark Barolak <mbxx@users.noreply.github.com>
  - 111ca7060a6ff50115ca85b59f6b5d8c8c5e9105 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 389ec3f906f018661a5308458d623d01f96d7b23 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 8fbcdb90952c57828c4a9c2f6d79fcd7cae9088f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 455dc17ba1af9635f0b60155bc565bc572a1e722 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f197d7c72a54064cfde5a2058f1513a4a0ee36fb Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 284378a71b32dfb3af4e3661f585e671d1b603a3 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>

GitOrigin-RevId: 9ee91d3e430fb33a4590486573792eb0fa146c2d
Change-Id: Ia06e548bc106cc9d136f6c65714be6645317aced

1 files changed, 385 insertions, 0 deletions

diff --git a/absl/flags/internal/commandlineflag.h b/absl/flags/internal/commandlineflag.h
new file mode 100644
index 00000000..382553d2
--- /dev/null
+++ b/absl/flags/internal/commandlineflag.h
@@ -0,0 +1,385 @@
+//
+// Copyright 2019 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
+//
+//      https://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 ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
+#define ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
+
+#include <atomic>
+
+#include "absl/base/macros.h"
+#include "absl/flags/marshalling.h"
+#include "absl/synchronization/mutex.h"
+#include "absl/types/optional.h"
+
+namespace absl {
+inline namespace lts_2019_08_08 {
+namespace flags_internal {
+
+// Type-specific operations, eg., parsing, copying, etc. are provided
+// by function specific to that type with a signature matching FlagOpFn.
+enum FlagOp {
+  kDelete,
+  kClone,
+  kCopy,
+  kCopyConstruct,
+  kSizeof,
+  kParse,
+  kUnparse
+};
+using FlagOpFn = void* (*)(FlagOp, const void*, void*);
+using FlagMarshallingOpFn = void* (*)(FlagOp, const void*, void*, void*);
+
+// Options that control SetCommandLineOptionWithMode.
+enum FlagSettingMode {
+  // update the flag's value unconditionally (can call this multiple times).
+  SET_FLAGS_VALUE,
+  // update the flag's value, but *only if* it has not yet been updated
+  // with SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef".
+  SET_FLAG_IF_DEFAULT,
+  // set the flag's default value to this.  If the flag has not been updated
+  // yet (via SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef")
+  // change the flag's current value to the new default value as well.
+  SET_FLAGS_DEFAULT
+};
+
+// Options that control SetFromString: Source of a value.
+enum ValueSource {
+  // Flag is being set by value specified on a command line.
+  kCommandLine,
+  // Flag is being set by value specified in the code.
+  kProgrammaticChange,
+};
+
+// Signature for the help generation function used as an argument for the
+// absl::Flag constructor.
+using HelpGenFunc = std::string (*)();
+
+// Signature for the function generating the initial flag value based (usually
+// based on default value supplied in flag's definition)
+using InitialValGenFunc = void* (*)();
+
+struct CommandLineFlagInfo;
+
+// Signature for the mutation callback used by watched Flags
+// The callback is noexcept.
+// TODO(rogeeff): add noexcept after C++17 support is added.
+using FlagCallback = void (*)();
+
+using FlagValidator = bool (*)();
+
+extern const char kStrippedFlagHelp[];
+
+// The per-type function
+template <typename T>
+void* FlagOps(FlagOp op, const void* v1, void* v2) {
+  switch (op) {
+    case kDelete:
+      delete static_cast<const T*>(v1);
+      return nullptr;
+    case kClone:
+      return new T(*static_cast<const T*>(v1));
+    case kCopy:
+      *static_cast<T*>(v2) = *static_cast<const T*>(v1);
+      return nullptr;
+    case kCopyConstruct:
+      new (v2) T(*static_cast<const T*>(v1));
+      return nullptr;
+    case kSizeof:
+      return reinterpret_cast<void*>(sizeof(T));
+    default:
+      return nullptr;
+  }
+}
+
+template <typename T>
+void* FlagMarshallingOps(FlagOp op, const void* v1, void* v2, void* v3) {
+  switch (op) {
+    case kParse: {
+      // initialize the temporary instance of type T based on current value in
+      // destination (which is going to be flag's default value).
+      T temp(*static_cast<T*>(v2));
+      if (!absl::ParseFlag<T>(*static_cast<const absl::string_view*>(v1), &temp,
+                              static_cast<std::string*>(v3))) {
+        return nullptr;
+      }
+      *static_cast<T*>(v2) = std::move(temp);
+      return v2;
+    }
+    case kUnparse:
+      *static_cast<std::string*>(v2) =
+          absl::UnparseFlag<T>(*static_cast<const T*>(v1));
+      return nullptr;
+    default:
+      return nullptr;
+  }
+}
+
+// Functions that invoke flag-type-specific operations.
+inline void Delete(FlagOpFn op, const void* obj) {
+  op(flags_internal::kDelete, obj, nullptr);
+}
+
+inline void* Clone(FlagOpFn op, const void* obj) {
+  return op(flags_internal::kClone, obj, nullptr);
+}
+
+inline void Copy(FlagOpFn op, const void* src, void* dst) {
+  op(flags_internal::kCopy, src, dst);
+}
+
+inline void CopyConstruct(FlagOpFn op, const void* src, void* dst) {
+  op(flags_internal::kCopyConstruct, src, dst);
+}
+
+inline bool Parse(FlagMarshallingOpFn op, absl::string_view text, void* dst,
+                  std::string* error) {
+  return op(flags_internal::kParse, &text, dst, error) != nullptr;
+}
+
+inline std::string Unparse(FlagMarshallingOpFn op, const void* val) {
+  std::string result;
+  op(flags_internal::kUnparse, val, &result, nullptr);
+  return result;
+}
+
+inline size_t Sizeof(FlagOpFn op) {
+  // This sequence of casts reverses the sequence from base::internal::FlagOps()
+  return static_cast<size_t>(reinterpret_cast<intptr_t>(
+      op(flags_internal::kSizeof, nullptr, nullptr)));
+}
+
+// The following struct contains the locks in a CommandLineFlag struct.
+// They are in a separate struct that is lazily allocated to avoid problems
+// with static initialization and to avoid multiple allocations.
+struct CommandLineFlagLocks {
+  absl::Mutex primary_mu;   // protects several fields in CommandLineFlag
+  absl::Mutex callback_mu;  // used to serialize callbacks
+};
+
+// Holds either a pointer to help text or a function which produces it.  This is
+// needed for supporting both static initialization of Flags while supporting
+// the legacy registration framework.  We can't use absl::variant<const char*,
+// const char*(*)()> since anybody passing 0 or nullptr in to a CommandLineFlag
+// would find an ambiguity.
+class HelpText {
+ public:
+  static constexpr HelpText FromFunctionPointer(const HelpGenFunc fn) {
+    return HelpText(fn, nullptr);
+  }
+  static constexpr HelpText FromStaticCString(const char* msg) {
+    return HelpText(nullptr, msg);
+  }
+
+  std::string GetHelpText() const;
+
+  HelpText() = delete;
+  HelpText(const HelpText&) = default;
+  HelpText(HelpText&&) = default;
+
+ private:
+  explicit constexpr HelpText(const HelpGenFunc fn, const char* msg)
+      : help_function_(fn), help_message_(msg) {}
+
+  HelpGenFunc help_function_;
+  const char* help_message_;
+};
+
+// Holds all information for a flag.
+struct CommandLineFlag {
+  constexpr CommandLineFlag(
+      const char* name_arg, HelpText help_text, const char* filename_arg,
+      const flags_internal::FlagOpFn op_arg,
+      const flags_internal::FlagMarshallingOpFn marshalling_op_arg,
+      const flags_internal::InitialValGenFunc initial_value_gen,
+      const bool retired_arg, void* def_arg, void* cur_arg)
+      : name(name_arg),
+        help(help_text),
+        filename(filename_arg),
+        op(op_arg),
+        marshalling_op(marshalling_op_arg),
+        make_init_value(initial_value_gen),
+        retired(retired_arg),
+        inited(false),
+        modified(false),
+        on_command_line(false),
+        validator(nullptr),
+        callback(nullptr),
+        def(def_arg),
+        cur(cur_arg),
+        counter(0),
+        atomic(kAtomicInit),
+        locks(nullptr) {}
+
+  // Revert the init routine.
+  void Destroy() const;
+
+  // Not copyable/assignable.
+  CommandLineFlag(const CommandLineFlag&) = delete;
+  CommandLineFlag& operator=(const CommandLineFlag&) = delete;
+
+  absl::string_view Name() const { return name; }
+  std::string Help() const { return help.GetHelpText(); }
+  bool IsRetired() const { return this->retired; }
+  bool IsModified() const;
+  void SetModified(bool is_modified);
+  bool IsSpecifiedOnCommandLine() const;
+  // Returns true iff this is a handle to an Abseil Flag.
+  bool IsAbseilFlag() const {
+    // Set to null for V1 flags
+    return this->make_init_value != nullptr;
+  }
+
+  absl::string_view Typename() const;
+  std::string Filename() const;
+  std::string DefaultValue() const;
+  std::string CurrentValue() const;
+
+  bool HasValidatorFn() const;
+  bool SetValidatorFn(FlagValidator fn);
+  bool InvokeValidator(const void* value) const;
+
+  // Return true iff flag has type T.
+  template <typename T>
+  inline bool IsOfType() const {
+    return this->op == &flags_internal::FlagOps<T>;
+  }
+
+  // Attempts to retrieve the flag value. Returns value on success,
+  // absl::nullopt otherwise.
+  template <typename T>
+  absl::optional<T> Get() const {
+    if (IsRetired() || flags_internal::FlagOps<T> != this->op)
+      return absl::nullopt;
+
+    T res;
+    Read(&res, flags_internal::FlagOps<T>);
+
+    return res;
+  }
+
+  void SetCallback(const flags_internal::FlagCallback mutation_callback);
+  void InvokeCallback();
+
+  // Sets the value of the flag based on specified std::string `value`. If the flag
+  // was successfully set to new value, it returns true. Otherwise, sets `error`
+  // to indicate the error, leaves the flag unchanged, and returns false. There
+  // are three ways to set the flag's value:
+  //  * Update the current flag value
+  //  * Update the flag's default value
+  //  * Update the current flag value if it was never set before
+  // The mode is selected based on `set_mode` parameter.
+  bool SetFromString(absl::string_view value,
+                     flags_internal::FlagSettingMode set_mode,
+                     flags_internal::ValueSource source, std::string* error);
+
+  void StoreAtomic(size_t size);
+
+  void CheckDefaultValueParsingRoundtrip() const;
+  // Invoke the flag validators for old flags.
+  // TODO(rogeeff): implement proper validators for Abseil Flags
+  bool ValidateDefaultValue() const;
+  bool ValidateInputValue(absl::string_view value) const;
+
+  // Constant configuration for a particular flag.
+ private:
+  const char* const name;
+  const HelpText help;
+  const char* const filename;
+
+ protected:
+  const FlagOpFn op;                         // Type-specific handler
+  const FlagMarshallingOpFn marshalling_op;  // Marshalling ops handler
+  const InitialValGenFunc make_init_value;   // Makes initial value for the flag
+  const bool retired;                        // Is the flag retired?
+  std::atomic<bool> inited;  // fields have been lazily initialized
+
+  // Mutable state (guarded by locks->primary_mu).
+  bool modified;            // Has flag value been modified?
+  bool on_command_line;     // Specified on command line.
+  FlagValidator validator;  // Validator function, or nullptr
+  FlagCallback callback;    // Mutation callback, or nullptr
+  void* def;                // Lazily initialized pointer to default value
+  void* cur;                // Lazily initialized pointer to current value
+  int64_t counter;            // Mutation counter
+
+  // For some types, a copy of the current value is kept in an atomically
+  // accessible field.
+  static const int64_t kAtomicInit = 0xababababababababll;
+  std::atomic<int64_t> atomic;
+
+  // Lazily initialized mutexes for this flag value.  We cannot inline a
+  // SpinLock or Mutex here because those have non-constexpr constructors and
+  // so would prevent constant initialization of this type.
+  // TODO(rogeeff): fix it once Mutex has constexpr constructor
+  struct CommandLineFlagLocks* locks;  // locks, laziliy allocated.
+
+  // Ensure that the lazily initialized fields of *flag have been initialized,
+  // and return the lock which should be locked when flag's state is mutated.
+  absl::Mutex* InitFlagIfNecessary() const;
+
+  // copy construct new value of flag's type in a memory referenced by dst
+  // based on current flag's value
+  void Read(void* dst, const flags_internal::FlagOpFn dst_op) const;
+  // updates flag's value to *src (locked)
+  void Write(const void* src, const flags_internal::FlagOpFn src_op);
+
+  friend class FlagRegistry;
+  friend class FlagPtrMap;
+  friend class FlagSaverImpl;
+  friend void FillCommandLineFlagInfo(CommandLineFlag* flag,
+                                      CommandLineFlagInfo* result);
+  friend bool TryParseLocked(CommandLineFlag* flag, void* dst,
+                             absl::string_view value, std::string* err);
+  friend absl::Mutex* InitFlag(CommandLineFlag* flag);
+};
+
+// Update any copy of the flag value that is stored in an atomic word.
+// In addition if flag has a mutation callback this function invokes it. While
+// callback is being invoked the primary flag's mutex is unlocked and it is
+// re-locked back after call to callback is completed. Callback invocation is
+// guarded by flag's secondary mutex instead which prevents concurrent callback
+// invocation. Note that it is possible for other thread to grab the primary
+// lock and update flag's value at any time during the callback invocation.
+// This is by design. Callback can get a value of the flag if necessary, but it
+// might be different from the value initiated the callback and it also can be
+// different by the time the callback invocation is completed.
+// Requires that *primary_lock be held in exclusive mode; it may be released
+// and reacquired by the implementation.
+void UpdateCopy(CommandLineFlag* flag);
+// Return true iff flag value was changed via direct-access.
+bool ChangedDirectly(CommandLineFlag* flag, const void* a, const void* b);
+
+// This macro is the "source of truth" for the list of supported flag types we
+// expect to perform lock free operations on. Specifically it generates code,
+// a one argument macro operating on a type, supplied as a macro argument, for
+// each type in the list.
+#define ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(A) \
+  A(bool)                                         \
+  A(short)                                        \
+  A(unsigned short)                               \
+  A(int)                                          \
+  A(unsigned int)                                 \
+  A(long)                                         \
+  A(unsigned long)                                \
+  A(long long)                                    \
+  A(unsigned long long)                           \
+  A(double)                                       \
+  A(float)
+
+}  // namespace flags_internal
+}  // inline namespace lts_2019_08_08
+}  // namespace absl
+
+#endif  // ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_