1 /* 2 * Copyright (C) 2017 The Android Open Source Project 3 * 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 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 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. 15 */ 16 17 #ifndef NETUTILS_HANDLE_H 18 #define NETUTILS_HANDLE_H 19 20 #include <ostream> 21 22 namespace android { 23 namespace netdutils { 24 25 // Opaque, strongly typed wrapper for integer-like handles. 26 // Explicitly avoids implementing arithmetic operations. 27 // 28 // This class is intended to avoid common errors when reordering 29 // arguments to functions, typos and other cases where plain integer 30 // types would silently cover up the mistake. 31 // 32 // usage: 33 // DEFINE_HANDLE(ProductId, uint64_t); 34 // DEFINE_HANDLE(ThumbnailHash, uint64_t); 35 // void foo(ProductId p, ThumbnailHash th) {...} 36 // 37 // void test() { 38 // ProductId p(88); 39 // ThumbnailHash th1(100), th2(200); 40 // 41 // foo(p, th1); <- ok! 42 // foo(th1, p); <- disallowed! 43 // th1 += 10; <- disallowed! 44 // p = th2; <- disallowed! 45 // assert(th1 != th2); <- ok! 46 // } 47 template <typename T, typename TagT> 48 class Handle { 49 public: 50 constexpr Handle() = default; 51 constexpr Handle(const T& value) : mValue(value) {} 52 53 const T get() const { return mValue; } 54 55 bool operator==(const Handle& that) const { return get() == that.get(); } 56 bool operator!=(const Handle& that) const { return get() != that.get(); } 57 58 private: 59 T mValue; 60 }; 61 62 #define DEFINE_HANDLE(name, type) \ 63 struct _##name##Tag {}; \ 64 using name = ::android::netdutils::Handle<type, _##name##Tag>; 65 66 template <typename T, typename TagT> 67 inline std::ostream& operator<<(std::ostream& os, const Handle<T, TagT>& handle) { 68 return os << handle.get(); 69 } 70 71 } // namespace netdutils 72 } // namespace android 73 74 #endif /* NETUTILS_HANDLE_H */ 75
