1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
|
// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_FUNCTIONAL_OVERLOADED_H_
#define BASE_FUNCTIONAL_OVERLOADED_H_
namespace base {
// absl::visit() needs to be called with a functor object, such as
//
// struct Visitor {
// std::string operator()(const PackageA& source) {
// return "PackageA";
// }
//
// std::string operator()(const PackageB& source) {
// return "PackageB";
// }
// };
//
// absl::variant<PackageA, PackageB> var = PackageA();
// return absl::visit(Visitor(), var);
//
// `Overloaded` enables the above code to be written as:
//
// absl::visit(
// Overloaded{
// [](const PackageA& pack) { return "PackageA"; },
// [](const PackageB& pack) { return "PackageB"; },
// }, var);
//
// Note: Overloads must be implemented for all the variant options. Otherwise,
// there will be a compilation error.
//
// This struct inherits operator() method from all its base classes.
// Introduces operator() method from all its base classes into its definition.
template <typename... Callables>
struct Overloaded : Callables... {
using Callables::operator()...;
};
// Uses template argument deduction so that the `Overloaded` struct can be used
// without specifying its template argument. This allows anonymous lambdas
// passed into the `Overloaded` constructor.
template <typename... Callables>
Overloaded(Callables...) -> Overloaded<Callables...>;
} // namespace base
#endif // BASE_FUNCTIONAL_OVERLOADED_H_
|
