[#BloombergLP-bsls-AtomicUint64-testAndSwap]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bsls.adoc[bsls]::xref:BloombergLP/bsls/AtomicUint64.adoc[AtomicUint64]::testAndSwap
:relfileprefix: ../../../
:mrdocs:

Conditionally swap this value if it equals `compareValue`.

== Synopsis

Declared in `<bsls_atomic.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:BloombergLP/bsls/Types/Uint64.adoc[Types::Uint64]
testAndSwap(
    xref:BloombergLP/bsls/Types/Uint64.adoc[Types::Uint64] compareValue,
    xref:BloombergLP/bsls/Types/Uint64.adoc[Types::Uint64] swapValue);
----

== Description

Compare the value of this object to the specified `compareValue`. If they are equal, set the value of this atomic 64‐bit unsigned integer to the specified `swapValue`, otherwise leave this value unchanged. Return the previous value of this atomic unsigned integer, whether or not the swap occurred. Note that the entire test‐and‐swap operation is performed atomically.

== Return Value

previous value of this object

== Parameters

[cols="1,4"]
|===
| Name| Description
| *compareValue*
| expected current value of this object
| *swapValue*
| value to store if the comparison succeeds
|===


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