The index of the field type in `Type.oneofs`, for message or enumeration types. The first type has index 1; zero means the type is not in the list.
Generated from protobuf field <code>int32 oneof_index = 7;</code>
int $var:
$this
public function setOneofIndex($var) { GPBUtil::checkInt32($var); $this->oneof_index = $var; return $this; }