io.Reader

As mentioned above the io.Reader is an important interface in the language Go. A lot(if not all) functions that need to read from something take an io.Readeras input. To fulfill the interface a type needs to implement that one method.The writing side io.Writer, has the Write method.

If you think of a new type in your program or package and you make it fulfill the io.Readeror io.Writer interface, the whole standard Go library can be used on that type!