Impl() string
}

// direct channel operations when possible
type XChan chan int

func (c XChan) Send(x int) {
	c <- x
}

func (c XChan) Nbsend(x int) bool {
	select {
	case c <- x:
		return true
	default:
		return false
	}
	panic("nbsend")
}

func (c XChan) Recv() int {
	return <-c
}

func (c XChan) Nbrecv() (int, bool) {
	select {
	case x := <-c:
		return x, true