Go Interface Elegance

1. at first, generic interface definitions [from io pkg]

   type Reader interface {
     Read(p []byte) (n int, err error)
   }
   
   type Writer interface {
     Write(p []byte) (n int, err error)
   }
   
   type Seeker interface {
     Seek(offset int64, whence int) (int64, error)
   }
   
   type Closer interface {
     Close() error
   }

2. interface compositions

   type ReadWriter interface {
     Reader
     Writer
   }
   
   type ReadSeeker interface {
     Reader
     Seeker
   }
   
   type ReadCloser interface {
     Reader
     Closer
   }
   
   type WriteSeeker interface {
     Writer
     Seeker
   }
   
   type WriteCloser interface {
     Writer
     Closer
   }
   
   type ReadWriteSeeker interface {
     Reader
     Writer
     Seeker
   }
   
   type ReadWriteCloser interface {
     Reader
     Writer
     Closer
   }

3. implement the interface’s function

   type StructA struct {
   }
   
   func (p *StructA) Read(p []byte) (n int, err error) {
   }
   
   func (p *StructA) Write(p []byte) (n int, err error) {
   }
   
   func (p *StructA) Seek(offset int64, whence int) (int64, error){
   }
   
   type StructB struct {
   }
   
   func (p *StructB) Read(p []byte) (n int, err error) {
   }
   
   func (p *StructB) Write(p []byte) (n int, err error) {
   }
   
   func (p *StructB) Close() error {
   }

   struct StructA has implemented interfaces

   • Reader
   • Writer
   • Seeker
   • ReadWriter
   • ReadSeeker
   • WriteSeeker
   • ReadWriteSeeker

   struct StructA can work as a parameter on below functions

   func Func(p *Reader) (int, error);
   func Func(p *Writer) (int, error);
   func Func(p *Seeker) (int, error);
   func Func(p *ReadWriter) (int, error);
   func Func(p *ReadSeeker) (int, error);
   func Func(p *WriteSeeker) (int, error);
   func Func(p *ReadWriteSeeker) (int, error);

   struct StructB has implemented interfaces

   • Reader
   • Writer
   • Closer
   • ReadWriter
   • ReadCloser
   • WriteCloser
   • ReadWriteCloser

   struct StructB can work as a parameter on below functions

   func Func(p *Reader) (int, error);
   func Func(p *Writer) (int, error);
   func Func(p *Closer) (int, error);
   func Func(p *ReadWriter) (int, error);
   func Func(p *ReadCloser) (int, error);
   func Func(p *WriteCloser) (int, error);
   func Func(p *ReadWriteCloser) (int, error);

4. easy to add functions to implement new interface with same signatures.

KISS and DRY.