std::swap(std::pair)
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   template< class T1, class T2 > void swap( pair<T1,T2>& lhs, pair<T1,T2>& rhs );  | 
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Swaps the contents of lhs and rhs. Equivalent to lhs.swap(rhs).
Contents | 
[edit] Parameters
| lhs, rhs | - | pairs whose contents to swap | 
[edit] Return value
(none)
[edit] Exceptions
noexcept specification: (since C++11)
|   noexcept(noexcept(x.swap(y)))  | 
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