std::experimental::propagate_const::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 function does not participate in overload resolution unless U is implicitly convertible to T.

3) Assigns std::forward<U>(u) to this->t_.

This constructor does not participate in overload resolution unless 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.

[edit] 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

[edit] Return value

*this.