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1 | //===-- Standalone implementation of std::optional --------------*- C++ -*-===// |
---|---|
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | |
9 | #ifndef LLVM_LIBC_SRC___SUPPORT_CPP_OPTIONAL_H |
10 | #define LLVM_LIBC_SRC___SUPPORT_CPP_OPTIONAL_H |
11 | |
12 | #include "src/__support/CPP/type_traits.h" |
13 | #include "src/__support/CPP/utility.h" |
14 | #include "src/__support/macros/attributes.h" |
15 | #include "src/__support/macros/config.h" |
16 | |
17 | namespace LIBC_NAMESPACE_DECL { |
18 | namespace cpp { |
19 | |
20 | // Trivial nullopt_t struct. |
21 | struct nullopt_t { |
22 | LIBC_INLINE constexpr explicit nullopt_t() = default; |
23 | }; |
24 | |
25 | // nullopt that can be used and returned. |
26 | LIBC_INLINE_VAR constexpr nullopt_t nullopt{}; |
27 | |
28 | // This is very simple implementation of the std::optional class. It makes |
29 | // several assumptions that the underlying type is trivially constructible, |
30 | // copyable, or movable. |
31 | template <typename T> class optional { |
32 | template <typename U, bool = !is_trivially_destructible<U>::value> |
33 | struct OptionalStorage { |
34 | union { |
35 | char empty; |
36 | U stored_value; |
37 | }; |
38 | |
39 | bool in_use = false; |
40 | |
41 | LIBC_INLINE ~OptionalStorage() { reset(); } |
42 | |
43 | LIBC_INLINE constexpr OptionalStorage() : empty() {} |
44 | |
45 | template <typename... Args> |
46 | LIBC_INLINE constexpr explicit OptionalStorage(in_place_t, Args &&...args) |
47 | : stored_value(forward<Args>(args)...) {} |
48 | |
49 | LIBC_INLINE constexpr void reset() { |
50 | if (in_use) |
51 | stored_value.~U(); |
52 | in_use = false; |
53 | } |
54 | }; |
55 | |
56 | // The only difference is that this type U doesn't have a nontrivial |
57 | // destructor. |
58 | template <typename U> struct OptionalStorage<U, false> { |
59 | union { |
60 | char empty; |
61 | U stored_value; |
62 | }; |
63 | |
64 | bool in_use = false; |
65 | |
66 | LIBC_INLINE constexpr OptionalStorage() : empty() {} |
67 | |
68 | template <typename... Args> |
69 | LIBC_INLINE constexpr explicit OptionalStorage(in_place_t, Args &&...args) |
70 | : stored_value(forward<Args>(args)...) {} |
71 | |
72 | LIBC_INLINE constexpr void reset() { in_use = false; } |
73 | }; |
74 | |
75 | OptionalStorage<T> storage; |
76 | |
77 | public: |
78 | LIBC_INLINE constexpr optional() = default; |
79 | LIBC_INLINE constexpr optional(nullopt_t) {} |
80 | |
81 | LIBC_INLINE constexpr optional(const T &t) : storage(in_place, t) { |
82 | storage.in_use = true; |
83 | } |
84 | LIBC_INLINE constexpr optional(const optional &) = default; |
85 | |
86 | LIBC_INLINE constexpr optional(T &&t) : storage(in_place, move(t)) { |
87 | storage.in_use = true; |
88 | } |
89 | LIBC_INLINE constexpr optional(optional &&O) = default; |
90 | |
91 | template <typename... ArgTypes> |
92 | LIBC_INLINE constexpr optional(in_place_t, ArgTypes &&...Args) |
93 | : storage(in_place, forward<ArgTypes>(Args)...) { |
94 | storage.in_use = true; |
95 | } |
96 | |
97 | LIBC_INLINE constexpr optional &operator=(T &&t) { |
98 | storage = move(t); |
99 | return *this; |
100 | } |
101 | LIBC_INLINE constexpr optional &operator=(optional &&) = default; |
102 | |
103 | LIBC_INLINE constexpr optional &operator=(const T &t) { |
104 | storage = t; |
105 | return *this; |
106 | } |
107 | LIBC_INLINE constexpr optional &operator=(const optional &) = default; |
108 | |
109 | LIBC_INLINE constexpr void reset() { storage.reset(); } |
110 | |
111 | LIBC_INLINE constexpr const T &value() const & { |
112 | return storage.stored_value; |
113 | } |
114 | |
115 | LIBC_INLINE constexpr T &value() & { return storage.stored_value; } |
116 | |
117 | LIBC_INLINE constexpr explicit operator bool() const { |
118 | return storage.in_use; |
119 | } |
120 | LIBC_INLINE constexpr bool has_value() const { return storage.in_use; } |
121 | LIBC_INLINE constexpr const T *operator->() const { |
122 | return &storage.stored_value; |
123 | } |
124 | LIBC_INLINE constexpr T *operator->() { return &storage.stored_value; } |
125 | LIBC_INLINE constexpr const T &operator*() const & { |
126 | return storage.stored_value; |
127 | } |
128 | LIBC_INLINE constexpr T &operator*() & { return storage.stored_value; } |
129 | |
130 | LIBC_INLINE constexpr T &&value() && { return move(storage.stored_value); } |
131 | LIBC_INLINE constexpr T &&operator*() && { |
132 | return move(storage.stored_value); |
133 | } |
134 | }; |
135 | |
136 | } // namespace cpp |
137 | } // namespace LIBC_NAMESPACE_DECL |
138 | |
139 | #endif // LLVM_LIBC_SRC___SUPPORT_CPP_OPTIONAL_H |
140 |
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