打开和写入文件时出错

I want to open a file and write some text to it, however I get the following error:

.\hello.go:13: cannot use msg (type string) as type []byte in argument to f.Write

Here's my code so far:

package main

import (
    "os"
)

func printer(msg string) (err error) {
    f, err := os.Create("helloworld.txt")
    if err != nil {
        return err
    }
    defer f.Close()
    f.Write(msg)
    return err
}

func main() {
    printer("Hello World")
}

Use io.WriteString(f, msg), f.Write([]byte(msg)) or io.Copy(f, strings.NewReader(msg)).