about summary refs log tree commit diff
path: root/absl/base/macros.h
blob: afa30300bc3ec4d403ef9b5195a4d2ba3c200919 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
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 <cassert>
#include <cstddef>

#include "absl/base/port.h"

// ABSL_ARRAYSIZE()
//
// Returns the number 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.
#define ABSL_ARRAYSIZE(array) \
  (sizeof(::absl::macros_internal::ArraySizeHelper(array)))

namespace absl {
namespace macros_internal {
// Note: this internal template function declaration is used by ABSL_ARRAYSIZE.
// The function doesn't need a definition, as we only use its type.
template <typename T, size_t N>
auto ArraySizeHelper(const T (&array)[N]) -> char (&)[N];
}  // namespace macros_internal
}  // namespace absl

// 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 clang-tidy.
#if defined(__clang__) && __cplusplus >= 201103L
#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_