Understanding the Bridge Pattern in Go: Decoupling Shapes and Pens

Bridge Pattern (Bridge)

Definition

The Bridge pattern separates the abstraction from its implementation so that both can be extended independently.

Understanding

The word “bridge” suggests connecting two kinds of resources. In the example, Shape is the shape interface and Pen is the drawing‑tool interface. By linking each shape with a pen, many color‑shape combinations become possible.

Code

package main

import (
    "fmt"
)

// Shape interface
type Shape interface {
    Show()
}

// Circle implementation
type Circle struct {}
func (t Circle) Show() {
    fmt.Println("圆形")
}

// Square implementation
type Square struct {}
func (t Square) Show() {
    fmt.Println("正方形")
}

// Pen interface
type Pen interface {
    Draw()
}

// BlackPen implementation
type BlackPen struct {}
func (t BlackPen) Draw() {
    fmt.Println("黑色")
}

// YellowPen implementation
type YellowPen struct {}
func (t YellowPen) Draw() {
    fmt.Println("黄色")
}

// Bridge connects a Pen and a Shape
type Bridge struct {
    p Pen
    s Shape
}

func (t *Bridge) SetPen(p Pen) {
    t.p = p
}

func (t *Bridge) SetShape(s Shape) {
    t.s = s
}

func (t Bridge) Image() {
    t.p.Draw()
    t.s.Show()
    fmt.Println("------------")
}

func main() {
    b := Bridge{}
    b.SetPen(BlackPen{})
    b.SetShape(Circle{})
    b.Image()

    b.SetPen(BlackPen{})
    b.SetShape(Square{})
    b.Image()

    b.SetPen(YellowPen{})
    b.SetShape(Circle{})
    b.Image()

    b.SetPen(BlackPen{})
    b.SetShape(Circle{})
    b.Image()
    return
}
/*
黑色
圆形
------------
黑色
正方形
------------
黄色
圆形
------------
黑色
圆形
------------
*/

By calling the Set* functions, different color‑shape combinations can be assembled. The Bridge struct embodies the bridging concept, allowing the Pen and Shape resources to be extended independently, ultimately enabling countless possible variations.

Source code repository:

https://github.com/gofish2020/gopattern/tree/main/structure/bridge