external/bsd/kyua-cli/dist/utils/optional.hpp

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  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)