type Scanner struct {
  src,
  tokens string // let's pretend that tokens is a string.
  pos int
}

func NewScanner(tokens string) *Scanner {
    return &Scanner{tokens: tokens}
}

func (s *Scanner) Init(src string) {
    s.src = src
}

func (s *Scanner) Init(src string) {
    s.src = src
    s.pos = 0
}

func (s *Scanner) Init(src string) {
    s = &Scanner{src, s.tokens, 0, /* other properties */ }
}