[#XLOG_IS_ON_IMPL]
= XLOG_IS_ON_IMPL
:mrdocs:

Expects a fully qualified LogLevel enum value.

== Synopsis

Declared in `<folly/logging/xlog.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
#define XLOG_IS_ON_IMPL(level)

----

== Description

This helper macro invokes XLOG_IS_ON_IMPL_HELPER() to perform the real log level check, with a couple additions:

* If the log level is less than FOLLY_XLOG_MIN_LEVEL it evaluates to false to allow the compiler to completely optimize out the check and log message if the level is less than this compile‐time fixed constant.
* If the log level is fatal, this has an extra check at the end to ensure the compiler can detect that it always evaluates to true. This helps the compiler detect that statements like XCHECK(false) never return. Note that XLOG_IS_ON_IMPL_HELPER() must still be invoked first for fatal log levels in order to initialize folly::detail::custom::xlogFileScopeInfo.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *level*
| A fully qualified `folly::LogLevel` value.
|===


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