OOP中的表达类型组成

Question

假设我们要编写一个具有3种基本角色类型的RPG游戏：战斗机，法师和弓箭手。此外，我们还结合了骑士，圣骑士和游侠等角色类型。在TypeScript中，我们可以像这样描述字符接口：

    // fighter can fight
    // mage can cast
    // archer can shoot
    // paradin can cast and fight
    // knight can fight and shoot
    // ranger can cast and shoot

    type Fighter = {fight: () => string}
    type Mage = {cast: () => string}
    type Archer = {shoot: () => string}
    type Knight = Fighter & Archer
    type Paladin = Fighter & Mage
    type Ranger = Archer & Mage

问题是如何仅使用OOP技术来实现这些接口（假设我们正在使用主流的OOP语言，如C＃）？

我在没有行为重复的情况下用继承来表达这一点没有成功。目前，我看到的唯一方法是：

class Paladin {
  constructor(private fighter: Fighter, private mage: Mage) {}

  fight() {this.fighter.fight()}
  cast() {this.mage.cast()}
}

但是我不喜欢这种方法，因为任何时候我想要制造圣骑士，我还必须制造一个法师和一个基本上是同一个人的战士

Answer 1

也许尝试将您的构图推得更远。您只需要一种具有不同能力的类型，例如：

public class Hero
{
    private readonly string name;
    private readonly IEnumerable<IHeroAbility> abilities;

    public Hero(string name, [Optional] IEnumerable<IHeroAbility> abilities)
    {
        this.name = name;
        this.abilities = abilities ?? new List<IHeroAbility> { new OhCrap() };
    }

    public void Attack()
    {
        Console.WriteLine(name);

        foreach (var ability in abilities) ability.Execute();

        Console.WriteLine();
    }
}

现在准备将可用的能力：

public interface IHeroAbility
{
    void Execute();
}

public class SwingSwordAbility : IHeroAbility
{
    public void Execute()
    {
        Console.WriteLine("And with all his might the hero swung his sword down onto his opponent...");
    }
}

public class ShootArrowAbility : IHeroAbility
{
    public void Execute()
    {
        Console.WriteLine("The hero loads an arrow into his bow without blinking and launches it with fierce speed towards his opponant...");
    }
}

public class CastFireBallAbility : IHeroAbility
{
    public void Execute()
    {
        Console.WriteLine("The hero reaches deep into the underverse and hurls a ball of fire towards his opponant...");
    }
}

public class OhCrap : IHeroAbility
{
    public void Execute()
    {
        Console.WriteLine("The hero pats his pockets as if he forgot something at home...");
    }
}

然后撰写您的英雄类型：

class Program
{
    static void Main(string[] args)
    {
        IHeroAbility swingSwordAbility = new SwingSwordAbility();
        IHeroAbility shootArrowAbility = new ShootArrowAbility();
        IHeroAbility castFireBallAbility = new CastFireBallAbility();

        var fighter = new Hero("The Fighter", new[] { swingSwordAbility });
        fighter.Attack();

        var mage = new Hero("The Mage", abilities: new[] { castFireBallAbility });
        mage.Attack();

        var archer = new Hero("The Archer", abilities: new[] { shootArrowAbility });
        archer.Attack();

        var knight = new Hero("The Knight", abilities: new[] { swingSwordAbility, shootArrowAbility });
        knight.Attack();

        var paladin = new Hero("The Paladin", abilities: new[] { swingSwordAbility, castFireBallAbility });
        paladin.Attack();

        var ranger = new Hero("The Ranger",abilities: new[] { shootArrowAbility, castFireBallAbility });
        ranger.Attack();

    }
}

输出：

如果您想要更明确的操作组，可以将Hero类修改为类似以下内容：

public class Hero
{
    private readonly string name;
    private readonly IEnumerable<IHeroAbility> meleeAbilities;
    private readonly IEnumerable<IHeroAbility> magicAbilities;
    private readonly IEnumerable<IHeroAbility> rangedAbilities;

    private static IHeroAbility Crap = new OhCrap();

    public Hero(
        string name,
        [Optional] IEnumerable<IHeroAbility> meleeAbilities,
        [Optional] IEnumerable<IHeroAbility> magicAbilities,
        [Optional] IEnumerable<IHeroAbility> rangedAbilities)
    {
        this.name = name;

        var defaultAbilities = new List<IHeroAbility> { };
        this.meleeAbilities = meleeAbilities ?? defaultAbilities;
        this.magicAbilities = magicAbilities ?? defaultAbilities;
        this.rangedAbilities = rangedAbilities ?? defaultAbilities;
    }

    public void MeleeAttack()
    {
        var ability = meleeAbilities.Any() ? meleeAbilities.First() : Crap;

        Console.WriteLine(name);
        ability.Execute();
    }

    public void MagicAttack()
    {
        var ability = magicAbilities.Any() ? magicAbilities.First() : Crap;

        Console.WriteLine(name);
        ability.Execute();
    }

    public void RangedAttack()
    {
        var ability = rangedAbilities.Any() ? rangedAbilities.First() : Crap;

        Console.WriteLine(name);
        ability.Execute();
    }

}

然后您可以开始构建它，以合并更复杂的逻辑，例如具有与技能，冷却时间，技能选择等相关的成本。

希望这会有所帮助！