Go builder pattern

builder.go

// https://go.dev/play/p/JSWYXbjHBlM
package main

import "fmt"

type Fruit struct {
	name  string
	color string
	shape string
}

func NewFruit() Fruit {
	return Fruit{}
}

func NewFruitFromFruit(f Fruit) Fruit {
	nf := f // works only for simple types
	return nf
}

func (f Fruit) SetName(name string) Fruit {
	f.name = name
	return f
}

func (f Fruit) SetColor(color string) Fruit {
	f.color = color
	return f
}

func (f Fruit) SetShape(shape string) Fruit {
	f.shape = shape
	return f
}

func (f Fruit) Build() (Fruit, error) {
	if f.name == "" {
		return f, fmt.Errorf("name is required")
	}
	return f, nil
}

func main() {
	apple, _ := NewFruit().SetName("apple").SetColor("red").SetShape("round").Build()
	watermelon, _ := NewFruit().SetName("watermelon").SetColor("green").SetShape("round").Build()
	greenApple, _ := NewFruitFromFruit(apple).SetColor("green").Build()
	fmt.Printf("%+v\n", apple)
	fmt.Printf("%+v\n", watermelon)
	fmt.Printf("%+v\n", greenApple)
	if _, err := NewFruit().Build(); err != nil {
		fmt.Println(err)
	}
}