std::valarray::swap
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | void swap( valarray& other ); | ||
Swaps the contents with those of other.
Parameters
| other | - | another valarray to swap the contents with | 
Return value
(none)
Exceptions
| (none) | (until C++11) | 
| noexcept specification:   noexcept | (since C++11) |