std::experimental::observer_ptr<W>:: observer_ptr

From cppreference.com
constexpr observer_ptr ( ) noexcept ;
constexpr observer_ptr ( nullptr_t ) noexcept ;
(1) (library fundamentals TS v2)
constexpr explicit observer_ptr ( element_type * p ) noexcept ;
(2) (library fundamentals TS v2)
template < class W2 >
constexpr observer_ptr ( observer_ptr < W2 > other ) noexcept ;
(3) (library fundamentals TS v2)
observer_ptr ( const observer_ptr & other ) = default ;
(4) (library fundamentals TS v2)
(implicitly declared)
observer_ptr ( observer_ptr && other ) = default ;
(5) (library fundamentals TS v2)
(implicitly declared)
1) Constructs an observer_ptr that has no corresponding watched object.
2) Constructs an observer_ptr that watches p .
3) Constructs an observer_ptr that watches other. get ( ) . This overload participates in overload resolution only if W2 * is convertible to element_type * .
4,5) Implicitly declared copy and move constructors. Constructs an observer_ptr that watches other. get ( ) .

Parameters

p - a pointer to an object to watch
other - another observer_ptr to copy from