The Writer Interface

Writing bytes in various places is an extremely common use case in all computer programs.

• writing JSON to an HTTP output
• ones and zeros to a network router
• bits into a digital port to turn a light on
• encoded pixels to a printer
• or letters on a console

Go has a set of standard interfaces for the most common uses, such as writing or reading bytes.

This means that everyone who produces code that writes or reads bytes can use these existing interfaces.

Pithy

You should always try to use the io.Writer interface in your code to make it more modular it allows users to swap in whatever type they want and have it write there instead.

The most common:

• io.Writer to write to any destination
• io.Reader to read from any source

// How to see what required to meet an interface 
go doc io.Writer

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

io.Reader interface

Simply implement the Read method on your type (or wrap it in one that does) and you can pass it in interchangabley

strings.Reader()

Question

Why would you use something like strings.Reader()?

Answer

The purpose to wrap a string with the Read() method so it meets the interface requirements of io.Reader. Typically the Read() method is an abstraction for files, stdin, network connections - but strings.NewReader() is a nice helper to wrap a plain string in that same abstraction.