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78 lines
1.9 KiB
C
78 lines
1.9 KiB
C
/*
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* Copyright 2016 Facebook, Inc.
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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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* http://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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* GCC compatible wrappers around clang attributes.
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*
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* @author Dominik Gabi
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*/
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#pragma once
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#ifndef __has_cpp_attribute
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#define FOLLY_HAS_CPP_ATTRIBUTE(x) 0
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#else
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#define FOLLY_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
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#endif
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#ifndef __has_extension
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#define FOLLY_HAS_EXTENSION(x) 0
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#else
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#define FOLLY_HAS_EXTENSION(x) __has_extension(x)
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#endif
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/**
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* Fallthrough to indicate that `break` was left out on purpose in a switch
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* statement, e.g.
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*
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* switch (n) {
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* case 22:
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* case 33: // no warning: no statements between case labels
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* f();
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* case 44: // warning: unannotated fall-through
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* g();
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* FOLLY_FALLTHROUGH; // no warning: annotated fall-through
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* }
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*/
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#if FOLLY_HAS_CPP_ATTRIBUTE(clang::fallthrough)
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#define FOLLY_FALLTHROUGH [[clang::fallthrough]]
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#else
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#define FOLLY_FALLTHROUGH
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#endif
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/**
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* Nullable indicates that a return value or a parameter may be a `nullptr`,
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* e.g.
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*
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* int* FOLLY_NULLABLE foo(int* a, int* FOLLY_NULLABLE b) {
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* if (*a > 0) { // safe dereference
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* return nullptr;
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* }
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* if (*b < 0) { // unsafe dereference
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* return *a;
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* }
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* if (b != nullptr && *b == 1) { // safe checked dereference
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* return new int(1);
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* }
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* return nullptr;
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* }
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*/
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#if FOLLY_HAS_EXTENSION(nullability)
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#define FOLLY_NULLABLE _Nullable
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#else
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#define FOLLY_NULLABLE
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#endif
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