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.
Declared in <folly/Preprocessor.h>
#define FB_ONE_OR_NONE(a, ...)
| Name | Description |
|---|---|
| a | The token emitted when a second argument is present. |