Can you give an example of a situation where using interfaces helps structure the code?

Interfaces in Go help structure code by defining a set of methods that different types must implement, which facilitates extensibility and testing.

Example: suppose you have different types of data storage — database, cache, file system. You can define an interface Storage with a method Save(data string) error.

package main
import "fmt"

// Interface
type Storage interface {
    Save(data string) error
}

// Implementation for database
type DBStorage struct{}
func (db DBStorage) Save(data string) error {
    fmt.Println("Saving to database:", data)
    return nil
}

// Implementation for file system
type FileStorage struct{}
func (fs FileStorage) Save(data string) error {
    fmt.Println("Saving to file:", data)
    return nil
}

func process(s Storage, data string) {
    s.Save(data)
}

func main() {
    db := DBStorage{}
    file := FileStorage{}

    process(db, "data for DB")
    process(file, "data for file")
}

This approach allows writing code that works with the abstraction Storage, independent of specific implementations, which simplifies maintenance and testing.