Difference between os.File, io.Reader and os.Stdin
Multi tool use
Difference between os.File, io.Reader and os.Stdin
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
@Projjol
os.File is a concrete type, your file is a variable of that type, os.Stdin is also a variable of that same type. io.Reader is an interface type, the os.File type implements the io.Reader interface, therefore the values file and os.Stdin can be used as an argument to NewScanner.– mkopriva
23 mins ago
os.File
file
os.Stdin
io.Reader
os.File
io.Reader
file
os.Stdin
thanks @mkopriva
– Projjol
5 mins ago
thanks @Uvelichitel
– Projjol
4 mins ago
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
thanks @Himanshu
– Projjol
3 mins ago
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io.Reader is an interface. os.File and os.Stdin implement this interface having method Read() and can be used where io.Reader expected
– Uvelichitel
31 mins ago