Understand Decorator Design Pattern in Go with the help of a Coffee Shop Example | Go Code

Hey Folks, we are running a series of the design pattern available in the Go programming world. As of now we have discussed

1. Optional Design Pattern
2. Singleton Design Pattern

We will understand the Decorator pattern using a simple coffee example. Lets assume we are building a coffee biller machine where there can be many top-ups available on the coffee.

Youtube Video on the same topic with wider coverage of topics available here: https://www.youtube.com/watch?v=_6-ivxilTZQ

Let’s assume you ordered a simple coffee

Coffee Bill have two fields which is description and cost, so lets define the interface for it first

// Coffee represents the base component interface
type Coffee interface {
 GetDescription() string
 Cost() float64
}

Let’s build this interface with our concrete component

// SimpleCoffee represents the concrete component
type SimpleCoffee struct{}

func (c *SimpleCoffee) GetDescription() string {
 return "Simple Coffee"
}

func (c *SimpleCoffee) Cost() float64 {
 return 1.0
}

Coffee maker: do you want to add extra milk?

You: Yes

Let’s build the code for it too

// Milk represents a concrete decorator
type Milk struct {
 *CoffeeDecorator
}

func NewMilk(coffee Coffee) *Milk {
 return &Milk{&CoffeeDecorator{coffee}}
}

func (m *Milk) GetDescription() string {
 return m.CoffeeDecorator.GetDescription() + ", Milk"
}

func (m *Milk) Cost() float64 {
 return m.CoffeeDecorator.Cost() + 0.5
}

Coffee maker: Do you want extra sugar?

You: Yes

Let’s build the code for it too

// Sugar represents another concrete decorator
type Sugar struct {
 *CoffeeDecorator
}

func NewSugar(coffee Coffee) *Sugar {
 return &Sugar{&CoffeeDecorator{coffee}}
}

func (s *Sugar) GetDescription() string {
 return s.CoffeeDecorator.GetDescription() + ", Sugar"
}

func (s *Sugar) Cost() float64 {
 return s.CoffeeDecorator.Cost() + 0.25
}

Now let’s run the code and check the outout

func main() {
 // Create a simple coffee
 coffee := &SimpleCoffee{}

 // Add milk to the coffee
 coffeeWithMilk := NewMilk(coffee)

 // Add sugar to the coffee
 coffeeWithMilkAndSugar := NewSugar(coffeeWithMilk)

 // Print description and cost of the decorated coffee
 fmt.Println("Description:", coffeeWithMilkAndSugar.GetDescription())
 fmt.Println("Cost:", coffeeWithMilkAndSugar.Cost())
}

Output:

Description: Simple Coffee, Milk, Sugar
Cost: 1.75

Full Code Github Link: CodePiper/GO/design-patterns/decorator.go at main · arshad404/CodePiper (github.com)

Youtube Video Link: https://www.youtube.com/watch?v=_6-ivxilTZQ

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