Switchをinterfaceを利用することで消滅させるStrategyパターン

interaface以外にもmapで同様のことができる。

type Member struct {
	Level        int
	Agility      int
	MagicAttack  int
	Vitality     int
}

type MagicType interface {
	Name() string
	CostMagicPoint(member Member) int
	AttackPower(member Member) int
	CostTechnicalPoint(member Member) int
}

type Fire struct{}
type Shiden struct{}
type HellFire struct{}

func (Fire) Name() string {
	return "ファイア"
}

func (Fire) CostMagicPoint(member Member) int {
	return 2
}

func (Fire) AttackPower(member Member) int {
	return 20 + int(float64(member.Level)*0.5)
}

func (Fire) CostTechnicalPoint(member Member) int {
	return 0
}

func (Shiden) Name() string {
	return "紫電"
}

func (Shiden) CostMagicPoint(member Member) int {
	return 5 + int(float64(member.Level)*0.2)
}

func (Shiden) AttackPower(member Member) int {
	return 50 + int(float64(member.Agility)*1.5)
}

func (Shiden) CostTechnicalPoint(member Member) int {
	return 5
}

func (HellFire) Name() string {
	return "地獄の業火"
}

func (HellFire) CostMagicPoint(member Member) int {
	return 16
}

func (HellFire) AttackPower(member Member) int {
	return 200 + int(float64(member.MagicAttack)*0.5+float64(member.Vitality)*2)
}

func (HellFire) CostTechnicalPoint(member Member) int {
	return 20 + int(float64(member.Level)*0.4)
}

type Magic struct {
	MagicType MagicType
	Member    Member
}

func NewMagic(magicType MagicType, member Member) *Magic {
	return &Magic{
		MagicType: magicType,
		Member:    member,
	}
}

client.go

package main

import "fmt"

func main() {
	// Memberを生成します
	member := Member{
		Level:       10,
		Agility:     15,
		MagicAttack: 20,
		Vitality:    30,
	}

	// Fireを使ってMagicを生成します
	magic := NewMagic(Fire{}, member)

	fmt.Println("Magic name:", magic.MagicType.Name())
	fmt.Println("Magic point cost:", magic.MagicType.CostMagicPoint(magic.Member))
	fmt.Println("Magic attack power:", magic.MagicType.AttackPower(magic.Member))
	fmt.Println("Magic technical point cost:", magic.MagicType.CostTechnicalPoint(magic.Member))

	// Shidenを使ってMagicを生成します
	magic = NewMagic(Shiden{}, member)

	fmt.Println("\nMagic name:", magic.MagicType.Name())
	fmt.Println("Magic point cost:", magic.MagicType.CostMagicPoint(magic.Member))
	fmt.Println("Magic attack power:", magic.MagicType.AttackPower(magic.Member))
	fmt.Println("Magic technical point cost:", magic.MagicType.CostTechnicalPoint(magic.Member))

	// HellFireを使ってMagicを生成します
	magic = NewMagic(HellFire{}, member)

	fmt.Println("\nMagic name:", magic.MagicType.Name())
	fmt.Println("Magic point cost:", magic.MagicType.CostMagicPoint(magic.Member))
	fmt.Println("Magic attack power:", magic.MagicType.AttackPower(magic.Member))
	fmt.Println("Magic technical point cost:", magic.MagicType.CostTechnicalPoint(magic.Member))
}

リクエストからNewMagic()へのインジェクションはMapを使えば、switchやifを使う必要もなくなります。