2 * Copyright 2015-present Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
18 * GCC compatible wrappers around clang attributes.
20 * @author Dominik Gabi
25 #ifndef __has_attribute
26 #define FOLLY_HAS_ATTRIBUTE(x) 0
28 #define FOLLY_HAS_ATTRIBUTE(x) __has_attribute(x)
31 #ifndef __has_cpp_attribute
32 #define FOLLY_HAS_CPP_ATTRIBUTE(x) 0
34 #define FOLLY_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
37 #ifndef __has_extension
38 #define FOLLY_HAS_EXTENSION(x) 0
40 #define FOLLY_HAS_EXTENSION(x) __has_extension(x)
44 * Fallthrough to indicate that `break` was left out on purpose in a switch
49 * case 33: // no warning: no statements between case labels
51 * case 44: // warning: unannotated fall-through
53 * FOLLY_FALLTHROUGH; // no warning: annotated fall-through
56 #if FOLLY_HAS_CPP_ATTRIBUTE(fallthrough)
57 #define FOLLY_FALLTHROUGH [[fallthrough]]
58 #elif FOLLY_HAS_CPP_ATTRIBUTE(clang::fallthrough)
59 #define FOLLY_FALLTHROUGH [[clang::fallthrough]]
60 #elif FOLLY_HAS_CPP_ATTRIBUTE(gnu::fallthrough)
61 #define FOLLY_FALLTHROUGH [[gnu::fallthrough]]
63 #define FOLLY_FALLTHROUGH
67 * Maybe_unused indicates that a function, variable or parameter might or
68 * might not be used, e.g.
70 * int foo(FOLLY_MAYBE_UNUSED int x) {
78 #if FOLLY_HAS_CPP_ATTRIBUTE(maybe_unused)
79 #define FOLLY_MAYBE_UNUSED [[maybe_unused]]
80 #elif FOLLY_HAS_ATTRIBUTE(__unused__) || __GNUC__
81 #define FOLLY_MAYBE_UNUSED __attribute__((__unused__))
83 #define FOLLY_MAYBE_UNUSED
87 * Nullable indicates that a return value or a parameter may be a `nullptr`,
90 * int* FOLLY_NULLABLE foo(int* a, int* FOLLY_NULLABLE b) {
91 * if (*a > 0) { // safe dereference
94 * if (*b < 0) { // unsafe dereference
97 * if (b != nullptr && *b == 1) { // safe checked dereference
103 #if FOLLY_HAS_EXTENSION(nullability)
104 #define FOLLY_NULLABLE _Nullable
105 #define FOLLY_NONNULL _Nonnull
107 #define FOLLY_NULLABLE
108 #define FOLLY_NONNULL
112 * "Cold" indicates to the compiler that a function is only expected to be
113 * called from unlikely code paths. It can affect decisions made by the
114 * optimizer both when processing the function body and when analyzing
118 #define FOLLY_COLD __attribute__((__cold__))