Interfaces are great

They're honestly brilliant. Interfaces allow for simple, elegant programming. Let's use Java to get a quick idea of how to use interfaces.

package mypackage;

public interface Edible {
  public void eat();
}

Now, a Burger class to implement Edible.

package mypackage;

public class Burger implements Edible {
  public void eat() {
    System.out.println("Burgers, yum!");
  }
}

This means that we can use our Burger class wherever we see Edible, such as in method arguments!

The problem with interfaces

But let's say that we are using a library, and that library has a class called Salad. Here's what Salad looks like:

package theirpackage;

public class Salad {
  public void eat() {
    System.out.println("I'm being healthy!")
  }
}

So Salad has an eat() method, but because the other library doesn't even know about Edible interface exists, it obviously can't implement it. This problem has definitely been encountered before, so let's talk about how Go has fixed it.

How Go fixes interfaces

With how Go interfaces work, you don't need to declare an interface implementation. If you implement the proper methods, you implement the interface. This is very prominent in Go, and is a key feature. Let's use our previous example.

First, let's remake our Edible interface.

package mypackage

type Edible interface {
  Eat()
}

Now, let's make a Burger struct that implements Edible.

package mypackage

type Burger struct {}

// How to define a method in Go
func (b Burger) Eat() {
  fmt.Println("Burgers, yum!")
}

Notice that we never acknowledged Edible anywhere while we made the Burger struct. This is because any type that has an Eat() method associated with it is considered Edible. This means that even types from other libraries can be Edible, as long as they have an Eat() method!

This means that even this Salad struct from a different package is Edible.

package theirpackage

type Salad struct {}

func (s Salad) Eat() {
  fmt.Println("I'm being healthy!")
}

This shows just how awesome Golang is. I highly recommend watching their video, A Tour of Go, which shows all of the brilliant features that Go has to offer.