1 /*
2  * Copyright (C) 2019 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 #pragma once
18 
19 namespace android::hardware::automotive::hidl_utils {
20 
21 /**
22  * Helper functor to fetch results from multi-return HIDL calls.
23  * It's meant to be used in place of _hidl_cb callbacks.
24  *
25  * Please note extracting these return variables outside of the callback scope requires making
26  * a copy of each return variable. This may be costly for frequently called HIDL methods with
27  * non-negligible return object size. Please be cautious about performance when using this.
28  *
29  * Example usage:
30  *     Result result;
31  *     sp<ISomeInterface> iface;
32  *     hidlObject->someMethod(arg1, arg2, hidl_utils::fill(&result, &iface)).assertOk();
33  *     // use result and iface
34  */
35 template <typename... T>
36 struct fill : public std::function<void(const T&...)> {
37     /**
38      * Create _hidl_cb functor that copies the call arguments to specified pointers.
39      *
40      * \param args... Targets to copy the call arguments to
41      */
fillfill42     fill(T*... args) : mTargets(args...) {}
43 
operatorfill44     void operator()(const T&... args) { copy<0, T...>(args...); }
45 
46   private:
47     std::tuple<T*...> mTargets;
48 
49     template <int Pos, typename First>
copyfill50     inline void copy(const First& first) {
51         *std::get<Pos>(mTargets) = first;
52     }
53 
54     template <int Pos, typename First, typename... Rest>
copyfill55     inline void copy(const First& first, const Rest&... rest) {
56         *std::get<Pos>(mTargets) = first;
57         copy<Pos + 1, Rest...>(rest...);
58     }
59 };
60 
61 }  // namespace android::hardware::automotive::hidl_utils
62