cmp/path.go
func (si SliceIndex) Key() int {
	if si.xkey != si.ykey {
		return -1
	}
	return si.xkey
}
func (si SliceIndex) Key() int {
	if si.xkey != si.ykey {
		return -1
	}
	return si.xkey
}
func ( si SliceIndex ) Key ( ) int { if si . xkey != si . ykey { return - 1 } return si . xkey }
// Key is the index key; it may return -1 if in a split state
Key is the index key ; it may return - 1 if in a split state