[#FB_ONE_OR_NONE]
= FB_ONE_OR_NONE
:mrdocs:

FB_ONE_OR_NONE(hello, world) expands to hello and FB_ONE_OR_NONE(hello) expands to nothing. This macro is used to insert or eliminate text based on the presence of another argument.

== Synopsis

Declared in `<folly/Preprocessor.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
#define FB_ONE_OR_NONE(a, ...)

----

== Parameters

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


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