Bridge

Bridge decouples the implementation from the abstraction. The abstract base class can be subclassed to provide different implementations and allow implementation details to be modified easily. The interface, which is a bridge, helps in making the functionality of concrete classes independent from the interface implementer classes. The bridge patterns allow the implementation details to change at runtime.

The bridge pattern demonstrates the principle, preferring composition over inheritance. It helps in situations where one should subclass multiple times orthogonal to each other. Runtime binding of the application, mapping of orthogonal class hierarchies, and platform independence implementation are the scenarios where the bridge pattern can be applied.

The bridge pattern components are abstraction, refined abstraction, implementer, and concrete implementer. Abstraction is the interface implemented as an abstract class that clients invoke with the method on the concrete implementer. Abstraction maintains a has-a relationship with the implementation, instead of an is-a relationship. The has-a relationship is maintained by composition. Abstraction has a reference of the implementation. Refined abstraction provides more variations than abstraction.

Let's say IDrawShape is an interface with the drawShape method.  DrawShape implements the IDrawShape interface. We create an IContour bridge interface with the drawContour method. The contour class implements the IContour interface. The ellipse class will have a, b , r properties and drawShape (an instance of DrawShape). The ellipse class implements the contour bridge interface to implement the drawContour method. The  drawContour method calls the drawShape method on the drawShape instance.

The following code demonstrates the bridge implementation: 

//main package has examples shown
// in Hands-On Data Structures and algorithms with Go book
package main
// importing fmt package
import (
 "fmt"
)
//IDrawShape interface
type IDrawShape interface {
 drawShape(x[5] float32,y[5] float32)
}
//DrawShape struct
type DrawShape struct{}