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
22namespace android {
23namespace 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// }
47template <typename T, typename TagT>
48class 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
66template <typename T, typename TagT>
67inline 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