I was looking at NewScanner in the official go docs and it mentions the parameter to be passed to bufio.NewScanner should be of type io.Reader. However, the following works for me:

bufio.NewScanner

io.Reader

file, err := os.Open("filename")
scanner := bufio.NewScanner(file)


The same can be seen for os.Stdin as well. Given this what is the difference between os.File, os.Stdin and io.Reader ? Are they interchangeable?

os.Stdin

os.File

os.Stdin

io.Reader

os.File

file

os.Stdin

io.Reader

os.File

io.Reader

file

os.Stdin

1 Answer
1

This is because bufio.NewScanner has io.Reader as an argument.

bufio.NewScanner

io.Reader

func NewScanner(r io.Reader) *Scanner


and io.Reader is the interface that wraps the basic Read method.

io.Reader

type Reader interface {
Read(p byte) (n int, err error)
}


From the os package in Golang:

Open opens the named file for reading. If successful, methods on the
returned file can be used for reading; the associated file descriptor
has mode O_RDONLY. If there is an error, it will be of type
*PathError.

func Open(name string) (file *File, err error)


The returned value *os.File implements io.Reader.

*os.File

io.Reader

So whetever implements Reader interface can be passed as an argument to any method has io.Reader as an argument.

io.Reader

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