[#BloombergLP-balm-MetricRegistry-createUserDataKey]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/balm.adoc[balm]::xref:BloombergLP/balm/MetricRegistry.adoc[MetricRegistry]::createUserDataKey
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:mrdocs:

Return a new unique key that can be used to associate (via `setUserData`) and retrieve (via `userData`) a value with a metric (or group of metrics). Note that the returned key can be used by clients of `balm` to associate additional information with a metric.

== Synopsis

Declared in `<balm_metricregistry.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
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xref:BloombergLP/balm/MetricDescription/UserDataKey.adoc[MetricDescription::UserDataKey]
createUserDataKey();
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