std::experimental::propagate_const::propagate_const

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

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

1) Constructs an propagate_const, default-initializing this->t_.

2) Explicitly defaulted move constructor that move constructs this->t_ from p.t_.

3) Initializes this->t_ as if by direct-non-list-initialization from the expression std::move(pu.t_)

This constructor does not participate in overload resolution unless std::is_constructible<T, U&&>::value is true, and is explicit if and only if std::is_convertible<U&&, T>::value is false.

4) Initializes this->t_ as if by direct-non-list-initialization with the expression std::forward<U>(u).

This constructor does not participate in overload resolution unless std::is_constructible<T, U&&>::value is true and std::decay_t<U> is not a specialization of propagate_const. This constructor is explicit if and only if std::is_convertible<U&&, T>::value is false.

5) Copy constructor 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 initialize the contained pointer with