当直接用import的包名当参数传递给函数时，则会报“use of package ${package name} without selector ”。如下示例通过引用logwriter包向文件写入一条日志：

${GOPATH}/src/zkwatcher/logwriter/logwriter.go

package logwriter

import (
	"os"
)

type logwriter struct {
	filename string
}

func New(filename string) (*logwriter, error) {
	return &logwriter{filename}, nil
}

//实现io.Writer接口
func (w *logwriter) Write(p []byte) (n int, err error) {
	f, err := os.Create(w.filename)
	if err != nil {
		return 0, err
	}
	defer f.Close()
	return f.Write(p)
}

${GOPATH}/src/zkwatcher/packagewithoutselector.go

package main

import (
	"fmt"
	"io"
	"zkwatcher/logwriter"
)

func main() {
	s := "120024,1583893679,183.199.195.151,C03FD5AAB4CA\n"
	writer, err := logwriter.New("./logs/server.log")
	if err != nil {
		fmt.Printf("%v\n", err)
	}

	test1(writer, s)
	//test2(writer, s)
}

//错误
func test1(writer *logwriter, s string) {
	_, err := writer.Write([]byte(s))
	if err != nil {
		fmt.Printf("Failed to write to log, %v\n", err)
	}
}

//正确
func test2(writer io.Writer, s string) {
	_, err := writer.Write([]byte(s))
	if err != nil {
		fmt.Printf("Failed to write to log, %v\n", err)
	}
}

调用test1时直接以包名logwriter作参数，则会报错

# command-line-arguments
./packagewithoutselector.go:19:18: use of package logwriter without selector

调用test2时以io.Writer接口作参数，则调用正确。