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std::experi...al::optional(3) C++ Standard Libarystd::experi...al::optional(3) NAME std::experimental::optional - std::experimental::optional Synopsis Defined in header <experimental/optional> template< class T > (library fundamentals TS) class optional; The class template std::experimental::optional manages an optional contained value, i.e. a value that may or may not be present. A common use case for optional is the return value of a function that may fail. As opposed to other approaches, such as std::pair<T,bool>, optional handles expensive to construct objects well and is more readable, as the intent is ex- pressed explicitly. Any instance of optional<T> at any given point in time either con- tains a value or does not contain a value. If an optional<T> contains a value, the value is guaranteed to be allocated as part of the optional object footprint, i.e. no dynamic memory allocation ever takes place. Thus, an optional object models an object, not a pointer, even though the operator*() and operator->() are defined. When an object of type optional<T> is contextually converted to bool, the conversion returns true if the object contains a value and false if it does not contain a value. The optional object contains a value in the following conditions: * The object is initialized with a value of type T * The object is assigned from another optional that contains a value. The object does not contain a value in the following conditions: * The object is default-initialized. * The object is initialized with a value of std::experimen- tal::nullopt_t or an optional object that does not contain a value. * The object is assigned from a value of std::experimental::nul- lopt_t or from an optional that does not contain a value Template parameters T - the type of the value to manage initialization state for. The type must meet the requirements of Destructible Member types Member type Definition value_type T Member functions constructor constructs the optional object (public member function) destructor destroys the contained value, if there is one (public member function) operator= assigns contents (public member function) Observers operator-> accesses the contained value operator* (public member function) operator bool checks whether the object contains a value (public member function) value returns the contained value (public member function) value_or returns the contained value if available, another value otherwise (public member function) Modifiers swap exchanges the contents (public member function) emplace constructs the contained value in-place (public member function) Member objects Member name Definition val (private) pointer to the contained value (which points at a data member of the same object), the name is for exposition only Non-member functions operator== operator!= operator< compares optional objects operator<= (function template) operator> operator>= make_optional creates an optional object (function template) std::swap(std::experimental::optional) specializes the std::swap al- gorithm (function) Helper classes std::hash<std::experimental::optional> specializes the std::hash al- gorithm (class template specializa- tion) nullopt_t indicator of optional type with uninitialized (library fundamentals TS) state (class) in_place_t disambiguation tag type for in-place (library fundamentals TS) construction of optional types (class) bad_optional_access exception indicating checked access to an (library fundamentals TS) optional that doesn't contain a value (class) Helper objects nullopt an object of type nullopt_t (library fundamentals TS) (function) in_place an object of type std::experimen- tal::in_place_t (library fundamentals TS) (function) http://cppreference.com 2022.07.31 std::experi...al::optional(3)
NAME | Synopsis | Template parameters | Member types | Member functions | Observers | Modifiers | Member objects | Non-member functions | Helper classes
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