| /* |
| * Copyright 2017 Facebook, Inc. |
| * |
| * 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. |
| */ |
| |
| /** |
| * GCC compatible wrappers around clang attributes. |
| * |
| * @author Dominik Gabi |
| */ |
| |
| #pragma once |
| |
| #ifndef __has_cpp_attribute |
| #define FOLLY_HAS_CPP_ATTRIBUTE(x) 0 |
| #else |
| #define FOLLY_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x) |
| #endif |
| |
| #ifndef __has_extension |
| #define FOLLY_HAS_EXTENSION(x) 0 |
| #else |
| #define FOLLY_HAS_EXTENSION(x) __has_extension(x) |
| #endif |
| |
| /** |
| * Fallthrough to indicate that `break` was left out on purpose in a switch |
| * statement, e.g. |
| * |
| * switch (n) { |
| * case 22: |
| * case 33: // no warning: no statements between case labels |
| * f(); |
| * case 44: // warning: unannotated fall-through |
| * g(); |
| * FOLLY_FALLTHROUGH; // no warning: annotated fall-through |
| * } |
| */ |
| #if FOLLY_HAS_CPP_ATTRIBUTE(clang::fallthrough) |
| #define FOLLY_FALLTHROUGH [[clang::fallthrough]] |
| #else |
| #define FOLLY_FALLTHROUGH |
| #endif |
| |
| /** |
| * Maybe_unused indicates that a function, variable or parameter might or |
| * might not be used, e.g. |
| * |
| * int foo(FOLLY_MAYBE_UNUSED int x) { |
| * #ifdef USE_X |
| * return x; |
| * #else |
| * return 0; |
| * #endif |
| * } |
| */ |
| #if FOLLY_HAS_CPP_ATTRIBUTE(__unused__) |
| #define FOLLY_MAYBE_UNUSED __attribute__((__unused__)) |
| #else |
| #define FOLLY_MAYBE_UNUSED |
| #endif |
| |
| /** |
| * Nullable indicates that a return value or a parameter may be a `nullptr`, |
| * e.g. |
| * |
| * int* FOLLY_NULLABLE foo(int* a, int* FOLLY_NULLABLE b) { |
| * if (*a > 0) { // safe dereference |
| * return nullptr; |
| * } |
| * if (*b < 0) { // unsafe dereference |
| * return *a; |
| * } |
| * if (b != nullptr && *b == 1) { // safe checked dereference |
| * return new int(1); |
| * } |
| * return nullptr; |
| * } |
| */ |
| #if FOLLY_HAS_EXTENSION(nullability) |
| #define FOLLY_NULLABLE _Nullable |
| #define FOLLY_NONNULL _Nonnull |
| #else |
| #define FOLLY_NULLABLE |
| #define FOLLY_NONNULL |
| #endif |