How to Implement the error Interface in Go

Implement the error interface by defining a type with a method named Error that returns a string. Any type with this method automatically satisfies the interface.

type MyError struct {
	msg string
}

func (e MyError) Error() string {
	return e.msg
}

func main() {
	var err error = MyError{"something went wrong"}
	fmt.Println(err) // prints: something went wrong
}

In Go, an interface is a contract that a type must fulfill to be used in specific ways. To make your custom error work with standard error handling, you just need to add a method called Error that returns a text description. Think of it like a label on a box; as long as the box has a label that says what's inside, the system knows how to handle it.