Technical specifications
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals TS v2)
Library fundamentals 3 (library fundamentals TS v3)
Extensions for parallelism (parallelism TS)
Extensions for parallelism 2 (parallelism TS v2)
Extensions for concurrency (concurrency TS)
Concepts (concepts TS)
Ranges (ranges TS)
Mathematical special functions (special functions TR)
constexpr void swap(propagate_const & pt) noexcept(/* see below */);
(library fundamentals TS v2)

Swaps the wrapped pointer with that of pt. Let t_ designate the private data member that is the wrapped pointer-like object, then this function is equivalent to swap(t_, pt.t_), where the overload resolution for swap is performed among std::swap and any declaration found by the usual lookup rules, as described in Swappable.

The behavior is undefined if lvalues of T do not satisfy Swappable.

[edit] Parameters

pt - another propagate_const object to swap with

[edit] Exceptions

noexcept specification:  
noexcept(noexcept(swap(t_, pt.t_)))
The lookup for the identifier swap in the exception specification finds overloads described above, and does not find the member function itself, making the exception specification equivalent to C++17 std::is_nothrow_swappable.
(library fundamentals TS v2)
noexcept specification:  
(library fundamentals TS v3)

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3413 LFTSv2 the exception specification was ill-formed made well-formed