If set, gives the index of a oneof in the containing type's oneof_decl list. This field is a member of that oneof.
Generated from protobuf field <code>optional int32 oneof_index = 9;</code>
int $var:
$this
public function setOneofIndex($var) { GPBUtil::checkInt32($var); $this->oneof_index = $var; return $this; }