Go - Structs And Funcs Should Accept Interfaces And Return Concrete Types

Info

When working with struct definitions, functions, interfaces and such, always try to work with interfaces, rather than concrete types. Accept Interfaces, return concrete structs.

Example

package main
 
import "fmt"
 
// Define an interface
type Reader interface {
	Read() string
}
 
// Concrete type that implements Reader
type FileReader struct{}
 
func (f FileReader) Read() string {
	return "data from file"
}
 
// A function that ACCEPTS an interface but RETURNS a concrete type
func Process(r Reader) Result {
	data := r.Read()
	return Result{Content: data}
}
 
// A concrete return type
type Result struct {
	Content string
}
 
func main() {
	var r Reader = FileReader{}     // assign concrete to interface
	result := Process(r)            // function accepts interface, returns concrete
	fmt.Println(result.Content)     // prints: data from file
}