Functional Options

Golang does not provide optional arguments. Thus, we need to be a little creative here. A Porsche has four fields that are configurable.

type Porsche struct {
    Model  string
    Trim   string
    Color  string
    Wheels string
}

Let's create a function type that is basically a setter for Porsche. Along with it, we will create four setter factory, one for each field.

type Option func(*Porsche)

func Model(val string) Option {
  return func(p *Porsche) {
    p.Model = val
  }
}

func Trim(val string) Option {
  return func(p *Porsche) {
    p.Trim = val
  }
}

func Color(val string) Option {
  return func(p *Porsche) {
    p.Color = val
  }
}

func Wheels(val string) Option {
  return func(p *Porsche) {
    p.Wheels = val
  }
}

The constructor will use the setters to optionally set properties for Porsche.

func NewPorsche(setters ...Option) *Porsche {
  // Default configuration
  p := &Porsche{
    Model:  "911",
    Trim:   "Base",
    Color:  "GT Silver",
    Wheels: "Carrera",
  }

  for _, setter := range setters {
    setter(p)
  }

  return p
}

The expected usage will look like this.

func main() {
  NewPorsche(Trim("Turbo S"), Color("Carmine Red"))
}