3 Copyright (C) 2017 Free Software Foundation, Inc.
5 This file is part of GDB.
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>. */
20 #ifndef GDB_OPTIONAL_H
21 #define GDB_OPTIONAL_H
26 /* This class attempts to be a compatible subset of std::optional,
27 which is slated to be available in C++17. This class optionally
28 holds an object of some type -- by default it is constructed not
29 holding an object, but later the object can be "emplaced". This is
30 similar to using std::unique_ptr, but in-object allocation is
39 m_instantiated (false)
49 /* These aren't deleted in std::optional, but it was simpler to
50 delete them here, because currently the users of this class don't
51 need them, and making them depend on the definition of T is
52 somewhat complicated. */
53 optional (const optional
&other
) = delete;
54 optional
<T
> &operator= (const optional
&other
) = delete;
56 template<typename
... Args
>
57 void emplace (Args
&&... args
)
61 new (&m_item
) T (std::forward
<Args
>(args
)...);
62 m_instantiated
= true;
66 constexpr const T
*operator-> () const
67 { return std::addressof (this->get ()); }
70 { return std::addressof (this->get ()); }
72 constexpr const T
&operator* () const &
73 { return this->get (); }
76 { return this->get (); }
79 { return std::move (this->get ()); }
81 constexpr const T
&&operator* () const &&
82 { return std::move (this->get ()); }
84 constexpr explicit operator bool () const noexcept
85 { return m_instantiated
; }
87 constexpr bool has_value () const noexcept
88 { return m_instantiated
; }
92 /* Destroy the object. */
95 gdb_assert (m_instantiated
);
96 m_instantiated
= false;
100 /* The get operations have m_instantiated as a precondition. */
101 T
&get () noexcept
{ return m_item
; }
102 constexpr const T
&get () const noexcept
{ return m_item
; }
111 /* True if the object was ever emplaced. */
117 #endif /* GDB_OPTIONAL_H */
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