为什么Go的io包中没有RuneWriter接口？

Question

Go's io package contains (among others) the following interfaces:

type ByteReader interface {
        ReadByte() (c byte, err error)
}

type ByteScanner interface {
        ByteReader
        UnreadByte() error
}

type ByteWriter interface {
        WriteByte(c byte) error
}

type RuneReader interface {
        ReadRune() (r rune, size int, err error)
}

type RuneScanner interface {
        RuneReader
        UnreadRune() error
}

But there is no RuneWriter interface:

type RuneWriter interface {
        WriteRune(r rune) (size int, err error)
}

Is there a reason that RuneWriter is missing?

Answer 1

The Go authors define interfaces based on need. They do not define an interface for the purpose of filling out a grid of possible methods. This policy helps to keep the standard library small and simple.

I think they concluded that there's little need for the the RuneWriter interface because they didn't need it in the standard packages or other packages that they maintain.

There's been no demand for the interface outside of the Go team. There are no requests for the interface on the issue tracker, mail list, or the available recorded history for the irc channel.

The other interfaces referenced in the question are used in the standard packages or other packages that the Go authors maintain.

You can define the interface in your own package or code. This is a very useful feature that's somewhat unique to Go.