system/host/fidl/examples/example-9.fidl2

module example_9

enum EchoMe {
    zero = 0;
    one = 1;
}

interface Echo {
  0: Echo(uint32 @uint32) -> (uint32 response);
  1: Echo(uint64 @uint64) -> (uint64 response);
  2: Echo(EchoMe req) -> (EchoMe response);
  3: Echo(handle req) -> (handle response);
  4: Echo(handle<channel> req) -> (handle<channel> response);
}

const EchoMe favorite_echo = zero