Proposed resolution:
This wording is relative to N4529.
Edit [propagate_const.algorithms] as indicated:
-1- template <class T> constexpr void swap(propagate_const<T>& pt1, propagate_const<T>& pt2) noexcept(see below)-2- The constant-expression in the exception-specification is noexcept(
swap(pt1.t_, pt2.t_)pt1.swap(pt2)).-3- Effects:
swap(pt1.t_, pt2.t_)pt1.swap(pt2).