1 // Copyright 2010 Google Inc. 2 // All rights reserved. 3 // 4 // Redistribution and use in source and binary forms, with or without 5 // modification, are permitted provided that the following conditions are 6 // met: 7 // 8 // * Redistributions of source code must retain the above copyright 9 // notice, this list of conditions and the following disclaimer. 10 // * Redistributions in binary form must reproduce the above copyright 11 // notice, this list of conditions and the following disclaimer in the 12 // documentation and/or other materials provided with the distribution. 13 // * Neither the name of Google Inc. nor the names of its contributors 14 // may be used to endorse or promote products derived from this software 15 // without specific prior written permission. 16 // 17 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 18 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 19 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 20 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 21 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 22 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 23 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 27 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 29 /// \file utils/optional.hpp 30 /// Provides the utils::optional class. 31 /// 32 /// The class is provided as a separate module on its own to minimize 33 /// header-inclusion side-effects. 34 35 #if !defined(UTILS_OPTIONAL_HPP) 36 #define UTILS_OPTIONAL_HPP 37 38 #include <ostream> 39 40 41 namespace utils { 42 43 44 namespace detail { 45 46 47 /// Internal type-safe representation for the none type. 48 struct none_t {}; 49 50 51 } // namespace detail 52 53 54 /// The none value. 55 /// 56 /// This has internal linkage so it is OK to define it in the header file. 57 /// However, pointers to none from different translation units will be 58 /// different. Just don't do that. 59 const detail::none_t none = {}; 60 61 62 /// Holds a data value or none. 63 /// 64 /// This class allows users to represent values that may be uninitialized. 65 /// Instead of having to keep separate variables to track whether a variable is 66 /// supposed to have a value or not, this class allows multiplexing the 67 /// behaviors. 68 /// 69 /// This class is a simplified version of Boost.Optional. 70 template< class T > 71 class optional { 72 /// Internal representation of the optional data value. 73 T* _data; 74 75 public: 76 optional(void); 77 optional(utils::detail::none_t); 78 optional(const optional< T >&); 79 explicit optional(const T&); 80 ~optional(void); 81 82 optional& operator=(utils::detail::none_t); 83 optional& operator=(const T&); 84 optional& operator=(const optional< T >&); 85 86 bool operator==(const optional< T >&) const; 87 bool operator!=(const optional< T >&) const; 88 89 operator bool(void) const; 90 91 const T& get(void) const; 92 const T& get_default(const T&) const; 93 T& get(void); 94 }; 95 96 97 template< class T > 98 std::ostream& operator<<(std::ostream&, const optional< T >&); 99 100 101 template< class T > 102 optional< T > make_optional(const T&); 103 104 105 } // namespace utils 106 107 108 #endif // !defined(UTILS_OPTIONAL_HPP) 109