std::atomic_ref<T>::fetch_or
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                    < cpp | atomic | atomic ref
                    
                                                            
                    |   member only of  atomic_ref<Integral> specializations | 
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|   T fetch_or( T arg, std::memory_order order = std::memory_order_seq_cst ) const noexcept;  | 
(since C++20) | |
Atomically replaces the current value of the referenced object with the result of bitwise OR of the value and arg. This operation is a read-modify-write operation. Memory is affected according to the value of order.
Parameters
| arg | - | the other argument of bitwise OR | 
| order | - | memory order constraints to enforce | 
Return value
The value of the referenced object, immediately preceding the effects of this function.