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Diffstat (limited to 'absl/base/macros.h')
| -rw-r--r-- | absl/base/macros.h | 201 |
1 files changed, 201 insertions, 0 deletions
diff --git a/absl/base/macros.h b/absl/base/macros.h new file mode 100644 index 000000000000..259970fea89a --- /dev/null +++ b/absl/base/macros.h @@ -0,0 +1,201 @@ +// +// 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: macros.h +// ----------------------------------------------------------------------------- +// +// This header file defines the set of language macros used within Abseil code. +// For the set of macros used to determine supported compilers and platforms, +// see absl/base/config.h instead. +// +// This code is compiled directly on many platforms, including client +// platforms like Windows, Mac, and embedded systems. Before making +// any changes here, make sure that you're not breaking any platforms. +// + +#ifndef ABSL_BASE_MACROS_H_ +#define ABSL_BASE_MACROS_H_ + +#include <cstddef> + +#include "absl/base/port.h" + +// ABSL_ARRAYSIZE() +// +// Returns the # of elements in an array as a compile-time constant, which can +// be used in defining new arrays. If you use this macro on a pointer by +// mistake, you will get a compile-time error. +// +// Note: this template function declaration is used in defining arraysize. +// Note that the function doesn't need an implementation, as we only +// use its type. +namespace absl { +namespace macros_internal { +template <typename T, size_t N> +char (&ArraySizeHelper(T (&array)[N]))[N]; +} // namespace macros_internal +} // namespace absl +#define ABSL_ARRAYSIZE(array) \ + (sizeof(::absl::macros_internal::ArraySizeHelper(array))) + +// kLinkerInitialized +// +// An enum used only as a constructor argument to indicate that a variable has +// static storage duration, and that the constructor should do nothing to its +// state. Use of this macro indicates to the reader that it is legal to +// declare a static instance of the class, provided the constructor is given +// the absl::base_internal::kLinkerInitialized argument. +// +// Normally, it is unsafe to declare a static variable that has a constructor or +// a destructor because invocation order is undefined. However, if the type can +// be zero-initialized (which the loader does for static variables) into a valid +// state and the type's destructor does not affect storage, then a constructor +// for static initialization can be declared. +// +// Example: +// // Declaration +// explicit MyClass(absl::base_internal:LinkerInitialized x) {} +// +// // Invocation +// static MyClass my_global(absl::base_internal::kLinkerInitialized); +namespace absl { +namespace base_internal { +enum LinkerInitialized { + kLinkerInitialized = 0, +}; +} // namespace base_internal +} // namespace absl + +// ABSL_FALLTHROUGH_INTENDED +// +// Annotates implicit fall-through between switch labels, allowing a case to +// indicate intentional fallthrough and turn off warnings about any lack of a +// `break` statement. The ABSL_FALLTHROUGH_INTENDED macro should be followed by +// a semicolon and can be used in most places where `break` can, provided that +// no statements exist between it and the next switch label. +// +// Example: +// +// switch (x) { +// case 40: +// case 41: +// if (truth_is_out_there) { +// ++x; +// ABSL_FALLTHROUGH_INTENDED; // Use instead of/along with annotations +// // in comments +// } else { +// return x; +// } +// case 42: +// ... +// +// Notes: when compiled with clang in C++11 mode, the ABSL_FALLTHROUGH_INTENDED +// macro is expanded to the [[clang::fallthrough]] attribute, which is analysed +// when performing switch labels fall-through diagnostic +// (`-Wimplicit-fallthrough`). See clang documentation on language extensions +// for details: +// http://clang.llvm.org/docs/AttributeReference.html#fallthrough-clang-fallthrough +// +// When used with unsupported compilers, the ABSL_FALLTHROUGH_INTENDED macro +// has no effect on diagnostics. In any case this macro has no effect on runtime +// behavior and performance of code. +#ifdef ABSL_FALLTHROUGH_INTENDED +#error "ABSL_FALLTHROUGH_INTENDED should not be defined." +#endif + +// TODO(zhangxy): Use c++17 standard [[fallthrough]] macro, when supported. +#if defined(__clang__) && defined(__has_warning) +#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough") +#define ABSL_FALLTHROUGH_INTENDED [[clang::fallthrough]] +#endif +#elif defined(__GNUC__) && __GNUC__ >= 7 +#define ABSL_FALLTHROUGH_INTENDED [[gnu::fallthrough]] +#endif + +#ifndef ABSL_FALLTHROUGH_INTENDED +#define ABSL_FALLTHROUGH_INTENDED \ + do { \ + } while (0) +#endif + +// ABSL_DEPRECATED() +// +// Marks a deprecated class, struct, enum, function, method and variable +// declarations. The macro argument is used as a custom diagnostic message (e.g. +// suggestion of a better alternative). +// +// Example: +// +// class ABSL_DEPRECATED("Use Bar instead") Foo {...}; +// ABSL_DEPRECATED("Use Baz instead") void Bar() {...} +// +// Every usage of a deprecated entity will trigger a warning when compiled with +// clang's `-Wdeprecated-declarations` option. This option is turned off by +// default, but the warnings will be reported by go/clang-tidy. +#if defined(__clang__) && __cplusplus >= 201103L && defined(__has_warning) +#define ABSL_DEPRECATED(message) __attribute__((deprecated(message))) +#endif + +#ifndef ABSL_DEPRECATED +#define ABSL_DEPRECATED(message) +#endif + +// ABSL_BAD_CALL_IF() +// +// Used on a function overload to trap bad calls: any call that matches the +// overload will cause a compile-time error. This macro uses a clang-specific +// "enable_if" attribute, as described at +// http://clang.llvm.org/docs/AttributeReference.html#enable-if +// +// Overloads which use this macro should be bracketed by +// `#ifdef ABSL_BAD_CALL_IF`. +// +// Example: +// +// int isdigit(int c); +// #ifdef ABSL_BAD_CALL_IF +// int isdigit(int c) +// ABSL_BAD_CALL_IF(c <= -1 || c > 255, +// "'c' must have the value of an unsigned char or EOF"); +// #endif // ABSL_BAD_CALL_IF + +#if defined(__clang__) +# if __has_attribute(enable_if) +# define ABSL_BAD_CALL_IF(expr, msg) \ + __attribute__((enable_if(expr, "Bad call trap"), unavailable(msg))) +# endif +#endif + +// ABSL_ASSERT() +// +// In C++11, `assert` can't be used portably within constexpr functions. +// ABSL_ASSERT functions as a runtime assert but works in C++11 constexpr +// functions. Example: +// +// constexpr double Divide(double a, double b) { +// return ABSL_ASSERT(b != 0), a / b; +// } +// +// This macro is inspired by +// https://akrzemi1.wordpress.com/2017/05/18/asserts-in-constexpr-functions/ +#if defined(NDEBUG) +#define ABSL_ASSERT(expr) (false ? (void)(expr) : (void)0) +#else +#define ABSL_ASSERT(expr) \ + (ABSL_PREDICT_TRUE((expr)) ? (void)0 : [] { assert(false && #expr); }()) +#endif + +#endif // ABSL_BASE_MACROS_H_ |