Abseil Common Libraries (C++) (grcp 依赖)
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188 lines
9.2 KiB
188 lines
9.2 KiB
#ifndef ABSL_BASE_OPTIONS_H_ |
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#define ABSL_BASE_OPTIONS_H_ |
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// Copyright 2019 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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// |
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// ----------------------------------------------------------------------------- |
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// File: options.h |
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// ----------------------------------------------------------------------------- |
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// |
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// This file contains Abseil configuration options for setting specific |
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// implementations instead of letting Abseil determine which implementation to |
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// use at compile-time. Setting these options may be useful for package or build |
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// managers who wish to guarantee ABI stability within binary builds (which are |
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// otherwise difficult to enforce). |
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// |
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// *** IMPORTANT NOTICE FOR PACKAGE MANAGERS: It is important that |
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// maintainers of package managers who wish to package Abseil read and |
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// understand this file! *** |
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// |
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// Abseil contains a number of possible configuration endpoints, based on |
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// parameters such as the detected platform, language version, or command-line |
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// flags used to invoke the underlying binary. As is the case with all |
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// libraries, binaries which contain Abseil code must ensure that separate |
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// packages use the same compiled copy of Abseil to avoid a diamond dependency |
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// problem, which can occur if two packages built with different Abseil |
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// configuration settings are linked together. Diamond dependency problems in |
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// C++ may manifest as violations to the One Definition Rule (ODR) (resulting in |
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// linker errors), or undefined behavior (resulting in crashes). |
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// |
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// Diamond dependency problems can be avoided if all packages utilize the same |
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// exact version of Abseil. Building from source code with the same compilation |
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// parameters is the easiest way to avoid such dependency problems. However, for |
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// package managers who cannot control such compilation parameters, we are |
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// providing the file to allow you to inject ABI (Application Binary Interface) |
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// stability across builds. Settings options in this file will neither change |
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// API nor ABI, providing a stable copy of Abseil between packages. |
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// |
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// Care must be taken to keep options within these configurations isolated |
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// from any other dynamic settings, such as command-line flags which could alter |
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// these options. This file is provided specifically to help build and package |
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// managers provide a stable copy of Abseil within their libraries and binaries; |
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// other developers should not have need to alter the contents of this file. |
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// |
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// ----------------------------------------------------------------------------- |
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// Usage |
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// ----------------------------------------------------------------------------- |
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// |
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// For any particular package release, set the appropriate definitions within |
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// this file to whatever value makes the most sense for your package(s). Note |
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// that, by default, most of these options, at the moment, affect the |
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// implementation of types; future options may affect other implementation |
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// details. |
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// |
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// NOTE: the defaults within this file all assume that Abseil can select the |
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// proper Abseil implementation at compile-time, which will not be sufficient |
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// to guarantee ABI stability to package managers. |
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// |
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// ----------------------------------------------------------------------------- |
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// Type Compatibility Options |
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// ----------------------------------------------------------------------------- |
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// |
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// ABSL_OPTION_USE_STD_ANY |
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// |
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// This option controls whether absl::any is implemented as an alias to |
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// std::any, or as an independent implementation. |
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// |
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// A value of 0 means to use Abseil's implementation. This requires only C++11 |
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// support, and is expected to work on every toolchain we support. |
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// |
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// A value of 1 means to use an alias to std::any. This requires that all code |
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// using Abseil is built in C++17 mode or later. |
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// |
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// A value of 2 means to detect the C++ version being used to compile Abseil, |
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// and use an alias only if a working std::any is available. This option is |
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// useful when you are building your entire program, including all of its |
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// dependencies, from source. It should not be used otherwise -- for example, |
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// if you are distributing Abseil in a binary package manager -- since in |
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// mode 2, absl::any will name a different type, with a different mangled name |
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// and binary layout, depending on the compiler flags passed by the end user. |
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// For more info, see https://abseil.io/about/design/dropin-types. |
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// |
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// User code should not inspect this macro. To check in the preprocessor if |
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// absl::any is a typedef of std::any, use the feature macro ABSL_USES_STD_ANY. |
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#define ABSL_OPTION_USE_STD_ANY 2 |
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// ABSL_OPTION_USE_STD_OPTIONAL |
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// |
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// This option controls whether absl::optional is implemented as an alias to |
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// std::optional, or as an independent implementation. |
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// |
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// A value of 0 means to use Abseil's implementation. This requires only C++11 |
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// support, and is expected to work on every toolchain we support. |
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// |
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// A value of 1 means to use an alias to std::optional. This requires that all |
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// code using Abseil is built in C++17 mode or later. |
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// |
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// A value of 2 means to detect the C++ version being used to compile Abseil, |
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// and use an alias only if a working std::optional is available. This option |
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// is useful when you are building your program from source. It should not be |
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// used otherwise -- for example, if you are distributing Abseil in a binary |
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// package manager -- since in mode 2, absl::optional will name a different |
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// type, with a different mangled name and binary layout, depending on the |
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// compiler flags passed by the end user. For more info, see |
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// https://abseil.io/about/design/dropin-types. |
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// A value of 2 means to detect the C++ version being used to compile Abseil, |
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// and use an alias only if a working std::optional is available. This option |
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// should not be used when your program is not built from source -- for example, |
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// if you are distributing Abseil in a binary package manager -- since in mode |
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// 2, absl::optional will name a different template class, with a different |
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// mangled name and binary layout, depending on the compiler flags passed by the |
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// end user. |
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// |
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// User code should not inspect this macro. To check in the preprocessor if |
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// absl::optional is a typedef of std::optional, use the feature macro |
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// ABSL_USES_STD_OPTIONAL. |
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#define ABSL_OPTION_USE_STD_OPTIONAL 2 |
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// ABSL_OPTION_USE_STD_STRING_VIEW |
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// |
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// This option controls whether absl::string_view is implemented as an alias to |
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// std::string_view, or as an independent implementation. |
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// |
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// A value of 0 means to use Abseil's implementation. This requires only C++11 |
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// support, and is expected to work on every toolchain we support. |
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// |
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// A value of 1 means to use an alias to std::string_view. This requires that |
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// all code using Abseil is built in C++17 mode or later. |
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// |
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// A value of 2 means to detect the C++ version being used to compile Abseil, |
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// and use an alias only if a working std::string_view is available. This |
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// option is useful when you are building your program from source. It should |
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// not be used otherwise -- for example, if you are distributing Abseil in a |
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// binary package manager -- since in mode 2, absl::string_view will name a |
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// different type, with a different mangled name and binary layout, depending on |
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// the compiler flags passed by the end user. For more info, see |
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// https://abseil.io/about/design/dropin-types. |
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// |
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// User code should not inspect this macro. To check in the preprocessor if |
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// absl::string_view is a typedef of std::string_view, use the feature macro |
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// ABSL_USES_STD_STRING_VIEW. |
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#define ABSL_OPTION_USE_STD_STRING_VIEW 2 |
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// ABSL_OPTION_USE_STD_VARIANT |
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// |
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// This option controls whether absl::variant is implemented as an alias to |
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// std::variant, or as an independent implementation. |
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// |
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// A value of 0 means to use Abseil's implementation. This requires only C++11 |
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// support, and is expected to work on every toolchain we support. |
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// |
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// A value of 1 means to use an alias to std::variant. This requires that all |
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// code using Abseil is built in C++17 mode or later. |
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// |
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// A value of 2 means to detect the C++ version being used to compile Abseil, |
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// and use an alias only if a working std::variant is available. This option |
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// is useful when you are building your program from source. It should not be |
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// used otherwise -- for example, if you are distributing Abseil in a binary |
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// package manager -- since in mode 2, absl::variant will name a different |
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// type, with a different mangled name and binary layout, depending on the |
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// compiler flags passed by the end user. For more info, see |
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// https://abseil.io/about/design/dropin-types. |
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// |
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// User code should not inspect this macro. To check in the preprocessor if |
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// absl::variant is a typedef of std::variant, use the feature macro |
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// ABSL_USES_STD_VARIANT. |
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#define ABSL_OPTION_USE_STD_VARIANT 2 |
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#endif // ABSL_BASE_OPTIONS_H_
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