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std::nullopt_t(3)	      C++ Standard Libary	     std::nullopt_t(3)

NAME
       std::nullopt_t -	std::nullopt_t

Synopsis
	  Defined in header <optional>
	  struct nullopt_t;		(since C++17)

	  std::nullopt_t is an empty class type	used to	indicate optional type
       with
	  uninitialized	 state.	In particular, std::optional has a constructor
       with nullopt_t
	  as a single argument,	which creates an optional that does  not  con-
       tain a value.

	  std::nullopt_t must be a non-aggregate LiteralType and cannot	have a
       default
	  constructor or an initializer-list constructor.

	  It must have a constexpr constructor that takes some implementation-
       defined literal
	  type.

Notes
	  The constraints on nullopt_t's constructors exist to support both op
       = {}; and op =
	  nullopt; as the syntax for disengaging an optional object.

	  A possible implementation of this class is

	struct nullopt_t {
	    explicit constexpr nullopt_t(int) {}
	};

See also
	  nullopt an object of type nullopt_t
	  (C++17) (constant)

http://cppreference.com		  2022.07.31		     std::nullopt_t(3)

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