std::experimental::observer_ptr::observer_ptr

From cppreference.com
constexpr observer_ptr();
constexpr observer_ptr( nullptr_t );
(1) (library fundamentals TS v2)
explicit observer_ptr( element_type* p );
(2) (library fundamentals TS v2)
template<class W2>
observer_ptr( observer_ptr<W2> other );
(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 constructor does not participate in overload resolution unless 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

Exceptions

noexcept specification:  
noexcept