GoLang - why is logging to stdin valid?

log.New(os.Stdin, "in", 1).Println("TT")

The following code out stream looks like it should use stdout or stderr, but I'm using the stdin input stream.
It should go into some panic, but output to the console normally.

Why is this working fine?
I don't know why.

um Isn't stream input used to type on the keyboard? But since I input stream input to output, I don't think this should work. stdout:console,
stderr:console,
stdin:keyboard

TL;DR - From the source code:

var (
	Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
	Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
	Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
)

> Stdin, Stdout, and Stderr are open Files pointing to the standard
> input, standard output, and standard error file descriptors.

what this actually means is that Go treats Stdin, Stdout and Stderr the same, just as regular Files. and why shouldn't it? that's really just what they are. If you run echo sometext > /dev/stdin in your shell of choice, you'll see that this is valid and the text "sometext" will be printed to the terminal

Digging Deeper

Let's examine the log.New function declaration:

func New(out io.Writer, prefix string, flag int) *Logger

> New creates a new Logger. The out variable sets the destination to
> which log data will be written. The prefix appears at the beginning of
> each generated log line, or after the log header if the Lmsgprefix
> flag is provided. The flag argument defines the logging properties.

You can see that the first argument is the io.Writer interface - which is declared as :

type Writer interface {
	Write(p []byte) (n int, err error)
}

This effectively means that log.New accepts every struct that has a Write(p []byte) (n int, err error) method. And because os.Stdin is of type os.File, it matches the io.Writer interface specification and the signature of log.New.