Seastar
High performance C++ framework for concurrent servers
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variant_utils.hh
1/*
2 * This file is open source software, licensed to you under the terms
3 * of the Apache License, Version 2.0 (the "License"). See the NOTICE file
4 * distributed with this work for additional information regarding copyright
5 * ownership. You may not use this file except in compliance with the License.
6 *
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing,
12 * software distributed under the License is distributed on an
13 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14 * KIND, either express or implied. See the License for the
15 * specific language governing permissions and limitations
16 * under the License.
17 */
18/*
19 * Copyright (C) 2017 ScyllaDB.
20 */
21
22#pragma once
23
24#include <variant>
25
26namespace seastar {
27
29namespace internal {
30
31template<typename... Args>
32struct variant_visitor : Args... {
33 variant_visitor(Args&&... a) : Args(std::move(a))... {}
34 using Args::operator()...;
35};
36
37template<typename... Args> variant_visitor(Args&&...) -> variant_visitor<Args...>;
38
39}
41
44
51template <typename... Args>
52auto make_visitor(Args&&... args)
53{
54 return internal::variant_visitor<Args...>(std::forward<Args>(args)...);
55}
56
67template <typename Variant, typename... Args>
68inline auto visit(Variant&& variant, Args&&... args)
69{
70 static_assert(sizeof...(Args) > 0, "At least one lambda must be provided for visitation");
71 return std::visit(
72 make_visitor(std::forward<Args>(args)...),
73 variant);
74}
75
76namespace internal {
77template<typename... Args>
78struct castable_variant {
79 std::variant<Args...> var;
80
81 template<typename... SuperArgs>
82 operator std::variant<SuperArgs...>() && {
83 return std::visit([] (auto&& x) {
84 return std::variant<SuperArgs...>(std::move(x));
85 }, var);
86 }
87};
88}
89
90template<typename... Args>
91internal::castable_variant<Args...> variant_cast(std::variant<Args...>&& var) {
92 return {std::move(var)};
93}
94
95template<typename... Args>
96internal::castable_variant<Args...> variant_cast(const std::variant<Args...>& var) {
97 return {var};
98}
99
101
102}
auto make_visitor(Args &&... args)
Definition: variant_utils.hh:52
auto visit(Variant &&variant, Args &&... args)
Definition: variant_utils.hh:68
Seastar API namespace.
Definition: abort_on_ebadf.hh:26
STL namespace.