Composition Example

gistfile1.txt

import (
	"testing"

	"github.com/stretchr/testify/require"
)

type Fruit interface {
	Size() string
	Look() string
}

type Apple struct {
	size string
}

func (a Apple) Look() string {
	return a.size + "apple"
}
func (a Apple) Size() string {
	return a.size
}

type DefaultOrange struct {
	size string
}

func (d DefaultOrange) Look() string {
	return d.size + "default-orange" // The default fruit is orange
}

type MediumOrange struct {
	DefaultOrange
}

func (u MediumOrange) Size() string {
	return u.size
}

func Fruitify(f Fruit) Fruit {
	return f
}

func TestStructComposition(t *testing.T) {
	apple := Apple{}
	apple.size = "small"
	appleInterface := Fruitify(apple)

	require.Equal(t, appleInterface.Look(), "smallapple")
	require.Equal(t, appleInterface.Size(), "small")

	MediumOrange := MediumOrange{}
	MediumOrange.size = "medium"
	MediumOrangeInterface := Fruitify(MediumOrange)

	require.Equal(t, MediumOrangeInterface.Look(), "mediumdefault-orange")
	require.Equal(t, MediumOrangeInterface.Size(), "medium")
}