[#FB_ONE_OR_NONE]
= FB&lowbar;ONE&lowbar;OR&lowbar;NONE
:mrdocs:

FB&lowbar;ONE&lowbar;OR&lowbar;NONE(hello, world) expands to hello and FB&lowbar;ONE&lowbar;OR&lowbar;NONE(hello) expands to nothing&period; This macro is used to insert or eliminate text based on the presence of another argument&period;

== Synopsis

Declared in `&lt;folly&sol;Preprocessor&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
#define FB&lowbar;ONE&lowbar;OR&lowbar;NONE(a, ...)

----

== Parameters

[cols="1,4"]
|===
| Name| Description
| *a*
| The token emitted when a second argument is present&period;
|===


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