Application-side Interfaces in Go

README.md

Application-side Interfaces in Go

By moving the interface to the application-side (application.go), you can still set the implementation-specific configuration details when you instantiate your library structs. If the interface was implemented on the library-side then you would need to provide:

type DB interface {
  Get([]byte) ([]byte, error)
  Put([]byte, []byte) error
  CacheSize() int
  SetCacheSize(int)
  TurboMode() bool
  SetTurboMode(bool)
}

The extra configuration functions are implementation specific. The generalization of DBs occurs on the application-side (not the library-side) so it makes more sense to only specify the interface required by the application on the application-side.

application.go

package myapp

import "mylib"

// DB is a generic interface to a key/value store.
type DB interface {
  Get(key []byte) ([]byte, error)
  Put(key, value []byte) error
}

// Server represents a wrapper for accessing the DB (maybe over HTTP?).
type Server struct {
  db DB
}

func (s *Server) ListenAndServe() error {
  ...
}

func main() {
  // Initialize the specific implementation of DB that we want to use.
  db: &mylib.AwesomeDB{
    CacheSize: 1024,
    TurboMode: true,
  }

  // Attach it to the server.
  s := &Server{db: db}

  // Start the server.
  s.ListenAndServe()
}

library.go

package mylib

type AwesomeDB struct {
  CacheSize int
  TurboMode bool
}

func (db *DB) Get(key []byte) ([]byte, error) {
  ...
}

func (db *DB) Put(key, value []byte) error {
  ...
}