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std::atomic_ref<T>:: exchange

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atomic_ref::exchange
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Constants
value_type exchange ( value_type desired,

std:: memory_order order =

std:: memory_order_seq_cst ) const noexcept ;
(constexpr since C++26)

Atomically replaces the value of the referenced object with desired . The operation is a read-modify-write operation. Memory is affected according to the value of order .

This overload participates in overload resolution only if std:: is_const_v < T > is false .

Parameters

desired - value to assign
order - memory order constraints to enforce

Return value

The value of the referenced object before the call.

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 3508
( P3323R1 ) 		C++20 exchange was meaningless for const T constrained to accept only non-const T