std::experimental::propagate_const<T>:: operator=

From cppreference.com
constexpr propagate_const & operator = ( propagate_const && p ) = default ;
(1) (library fundamentals TS v2)
template < class U >
constexpr propagate_const & operator = ( propagate_const < U > && pu ) ;
(2) (library fundamentals TS v2)
template < class U >
constexpr propagate_const & operator = ( U && u ) ;
(3) (library fundamentals TS v2)
propagate_const & operator = ( const propagate_const & ) = delete ;
(4) (library fundamentals TS v2)

Let t_ designate the private data member that is the wrapped pointer-like object.

1) Explicitly defaulted move assignment operator that move assigns this - > t_ from p. t_ .
2) Assigns std :: move ( pu. t_ ) to this - > t_ .
This overload participates in overload resolution only if U is implicitly convertible to T .
3) Assigns std:: forward < U > ( u ) to this - > t_ .
This overload participates in overload resolution only if U is implicitly convertible to T and std:: decay_t < U > is not a specialization of propagate_const .
4) Copy assignment operator is explicitly deleted. propagate_const is non-copyable.

Parameters

p - another propagate_const object to move from
pu - another propagate_const object of a different specialization to move from
u - another object to assign to the contained pointer

Return value

* this .