Composition

Composition implements a "has-a" relationship. It allows a class to contain an object of another class.

Advantages

• Flexibility:
  
  Composition and interfaces allow for decoupled designs. You can change the components of a struct or the implementation of an interface without affecting other parts of your program.

• Simplicity:
  
  Avoiding classical inheritance can lead to simpler, more straightforward code. It encourages thinking in terms of what objects do (behaviors) rather than what they are in an inheritance hierarchy.

• Maintainability:
  
  Code that uses interfaces and composition is often easier to maintain and extend, as changes tend to be more localized.

Source: https://medium.com/@chaewonkong/go-composition-and-interfaces-a4b4346f8565