How to Dynamically Add Features in Go Using the Decorator Pattern

Decorator Pattern (Decorator)

Definition

It is a pattern that dynamically adds extra functionality to an object without changing its existing structure.

Understanding

For example, a date‑formatting function provides a generic method. When a new date format is needed, additional behavior can be added without modifying the original function, similar to decorating the function.

Another analogy: a woman who does not go out without makeup can become a “goddess” after careful decoration.

Or a bare‑bones house: the structural framework cannot be changed, but interior decoration can transform it into a luxurious home.

These examples show that the original object (woman, house, system function) remains unchanged; extra decorations enrich it, aligning with the Open/Closed Principle.

Code

First, define a generic interface:

type Showable interface {
    Show()
}

Implement a plain "girl" without makeup:

//普通的女生
type Girl struct {}

func (t *Girl) Show() {
    fmt.Print("素颜女生")
}

MakeUpDecorator adds a base layer of decoration:

//MakeUpDecorator 化妆
type MakeUpDecorator struct {
    Showable
}

func (t *MakeUpDecorator) Show() {
    fmt.Print("打粉底(")
    t.Showable.Show()
    fmt.Print(")")
}

LispDecorator adds lipstick on top of the previous decoration:

//LispDecorator 口红
type LispDecorator struct {
    Showable
}

func (t *LispDecorator) Show() {
    fmt.Print("涂口红(")
    t.Showable.Show()
    fmt.Print(")")
}

Putting it together:

func main() {
    //素颜女生
    girl := Girl{}
    girl.Show()
    fmt.Println("")
    //化妆后的女神
    l := LispDecorator{Showable: &MakeUpDecorator{Showable: &Girl{}}}
    l.Show()
    fmt.Println("")
    return
}

Output:

素颜女生
涂口红(打粉底(素颜女生))

The output demonstrates that the plain girl can go out without makeup, or she can be wrapped with multiple decorators to add behavior while the external call remains unchanged and transparent.

Source code address:

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