Builder Pattern missing parts

[Gil]

There are parts that you show in how to use the pattern that aren't in the example of creating it.

i.e. NewBuilder(), Paint(..), etc...

[zhangsu]

as @gcstang mentioned, builder pattern missing some code that we can't understand

[Ben Petersen]

Just ran into this as well. Looked promising, nice and clean, but it's incomplete. Once you get to this point:

assembly := car.NewBuilder().Paint(car.RedColor)

You'll have to go elsewhere to find the missing pieces.

[Zhong Qin]

According to the usage code. We should change Color(Color) Builder to Paint(Color) Builder. Thus,

type Builder interface {
	Paint(Color) Builder
	Wheels(Wheels) Builder
	TopSpeed(Speed) Builder
	Build() Interface
}

And the NewBuilder() should be:

func NewBuilder(b Builder) Builder {
	return b
}

Here, we assume that they are in the same package. Thus, the usage part should be:

import (
	"log"
	"testing"
)

// the implementation of Builder interface
type Car struct {
	color  Color
	wheels Wheels
	speed  Speed
}

func (c Car) Paint(color Color) Builder {
	c.color = color
	return c
}
func (c Car) Wheels(w Wheels) Builder {
	c.wheels = w
	return c
}
func (c Car) TopSpeed(s Speed) Builder {
	c.speed = s
	return c
}
func (c Car) Build() Interface {
	switch c.wheels {
	case SportsWheels:
		return SportsCar{}
	case SteelWheels:
		return FamilyCar{}
	}
	return nil
}

// the implementation of Interface interface
type FamilyCar struct{}

func (f FamilyCar) Drive() error {
	log.Println("FamilyCar Drive()")
	return nil
}
func (f FamilyCar) Stop() error {
	log.Println("FamilyCar Stop()")
	return nil
}

// the implementation of Interface interface
type SportsCar struct{}

func (s SportsCar) Drive() error {
	log.Println("SportsCar Drive()")
	return nil
}

func (s SportsCar) Stop() error {
	log.Println("SportsCar Stop()")
	return nil
}

// the testcase
func TestCarBuilder(t *testing.T) {
	assembly := NewBuilder(Car{}).Paint(RedColor)

	familyCar := assembly.Wheels(SportsWheels).TopSpeed(50 * MPH).Build()
	familyCar.Drive()
	familyCar.Stop()

	sportsCar := assembly.Wheels(SteelWheels).TopSpeed(150 * MPH).Build()
	sportsCar.Drive()
	sportsCar.Stop()

}

I also create a UML illustration of the demo code.

[Ben Petersen]

Very nice! Possibly could fork & PR to get it included? If PR not accepted, your fork would still be an improvement.