You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: buffer.go
    path of file: ./repos/macdriver/generate/declparse/lexer
    
    the code of the file until where you have to start completion: package lexer

import (
	"io"
)

// TokenBuffer represents a wrapper for scanner to add a buffer.
// It provides a fixed-length circular buffer that can be unread.
type TokenBuffer struct {
	IgnoreWhitespace bool

	s   *Scanner
	i   int // buffer index
	n   int // buffer size
	buf [6]struct {
		tok Token
    
func (s *TokenBuffer) ScanFunc(scan func() (Token, Pos, string)) (tok Token, pos Pos, lit string) {
	// If we have unread tokens then read them off the buffer first.
	if s.n > 0 {
		s.n--
		return s.Current()
	}

	tok, pos, lit = scan()

	if s.IgnoreWhitespace && tok == WS {
		tok, pos, lit = scan()
	}

	// Move buffer position forward and save the token.
	s.i = (s.i + 1) % len(s.buf)
	buf := &s.buf[s.i]
	buf.tok, buf.pos, buf.lit = tok, pos, lit

	return s.Current()
}