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: binary.go
    path of file: ./repos/scan4all/vendor/github.com/lunixbochs/struc
    
    the code of the file until where you have to start completion: package struc

import (
	"encoding/binary"
	"io"
	"reflect"
)

type byteWriter struct {
	buf []byte
	pos int
}

func (b byteWriter) Writ
    
func (b binaryFallback) Unpack(r io.Reader, val reflect.Value, options *Options) error {
	var order binary.ByteOrder = binary.BigEndian
	if options.Order != nil {
		order = options.Order
	}
	return binary.Read(r, order, val.Interface())
}