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
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
|
/*
* Copyright 2022 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <functional>
#include <optional>
#include <utility>
#include <ftl/details/optional.h>
namespace android::ftl {
// Superset of std::optional<T> with monadic operations, as proposed in https://wg21.link/P0798R8.
//
// TODO: Remove in C++23.
//
template <typename T>
struct Optional final : std::optional<T> {
using std::optional<T>::optional;
// Implicit downcast.
Optional(std::optional<T> other) : std::optional<T>(std::move(other)) {}
using std::optional<T>::has_value;
using std::optional<T>::value;
// Returns Optional<U> where F is a function that maps T to U.
template <typename F>
constexpr auto transform(F&& f) const& {
using R = details::transform_result_t<F, decltype(value())>;
if (has_value()) return R(std::invoke(std::forward<F>(f), value()));
return R();
}
template <typename F>
constexpr auto transform(F&& f) & {
using R = details::transform_result_t<F, decltype(value())>;
if (has_value()) return R(std::invoke(std::forward<F>(f), value()));
return R();
}
template <typename F>
constexpr auto transform(F&& f) const&& {
using R = details::transform_result_t<F, decltype(std::move(value()))>;
if (has_value()) return R(std::invoke(std::forward<F>(f), std::move(value())));
return R();
}
template <typename F>
constexpr auto transform(F&& f) && {
using R = details::transform_result_t<F, decltype(std::move(value()))>;
if (has_value()) return R(std::invoke(std::forward<F>(f), std::move(value())));
return R();
}
// Returns Optional<U> where F is a function that maps T to Optional<U>.
template <typename F>
constexpr auto and_then(F&& f) const& {
using R = details::and_then_result_t<F, decltype(value())>;
if (has_value()) return std::invoke(std::forward<F>(f), value());
return R();
}
template <typename F>
constexpr auto and_then(F&& f) & {
using R = details::and_then_result_t<F, decltype(value())>;
if (has_value()) return std::invoke(std::forward<F>(f), value());
return R();
}
template <typename F>
constexpr auto and_then(F&& f) const&& {
using R = details::and_then_result_t<F, decltype(std::move(value()))>;
if (has_value()) return std::invoke(std::forward<F>(f), std::move(value()));
return R();
}
template <typename F>
constexpr auto and_then(F&& f) && {
using R = details::and_then_result_t<F, decltype(std::move(value()))>;
if (has_value()) return std::invoke(std::forward<F>(f), std::move(value()));
return R();
}
};
template <typename T, typename U>
constexpr bool operator==(const Optional<T>& lhs, const Optional<U>& rhs) {
return static_cast<std::optional<T>>(lhs) == static_cast<std::optional<U>>(rhs);
}
template <typename T, typename U>
constexpr bool operator!=(const Optional<T>& lhs, const Optional<U>& rhs) {
return !(lhs == rhs);
}
// Deduction guides.
template <typename T>
Optional(T) -> Optional<T>;
template <typename T>
Optional(std::optional<T>) -> Optional<T>;
} // namespace android::ftl
|