{C#}干净的继承

背景

• 处理某项功能在多数子类共用，少数子类禁用。
• 平衡代码量，安全性(误用|拥有他类成员，隐藏他类控件仍会误用)，灵活性

客户代码

using static System.Console;

namespace CleanInheritance
{
    class Program
    {
        static readonly string _tiger = "Tiger", _swan = "Swan";

        static void Main(string[] args)
        {
            WriteLine("\nwrong case:");
            var tiger = new WrongAnimal(_tiger);
            tiger.Eat("deer");
            tiger.Run(100);
            var wrongSwan = new WrongAnimal(_swan);
            wrongSwan.Eat("grass");
            wrongSwan.Run(50);

            WriteLine("\nright case:");
            var rightTiger = new RightAnimal(_tiger);
            rightTiger.Eat("deer");
            rightTiger.Run(100);
            var rightSwan = new RightSwan(_swan);
            rightSwan.Eat("grass");
            rightSwan.Run(50);

            WriteLine("\nbetter case:");
            var betterTiger = new Beast(_tiger);
            betterTiger.Eat("deer");
            betterTiger.Run(100);
            var betterSwan = new Bird(_swan);
            betterSwan.Eat("grass");
            betterSwan.Fly(50);

            WriteLine("\nmore case:");
            var moreTiger = new MoreBeast(_tiger, new BeastSkill(_tiger));
            moreTiger.Eat("deer");
            moreTiger.Run(100);
            var moreSwan = new MoreBird(_swan, new BirdSkill(_swan));
            moreSwan.Eat("grass");
            moreSwan.Fly(50);
        }
    }
}

错误的处理

using static System.Console;

namespace CleanInheritance
{
    // 所有方法都归基类，由程序员(人)判断是否应该调用
    // 容易误调用，ex. swan.Run()
    // 代码量小，安全性差，灵活性差
    public class WrongAnimal
    {
        readonly string _name;

        public WrongAnimal(string name) => _name = name;

        public void Eat(string something)
            => WriteLine($"- {_name} is eating a/some {something}.");

        public void Run(int speed)
            => WriteLine($"- {_name} is running at {speed}km/h.");
    }
}

正确的处理

using static System.Console;

namespace CleanInheritance
{
    // 所有方法都归基类，但重写方法限制错误调用
    // 适用该方法公开
    // ex. swan.Run()时忽略|报错
    // 代码量中，安全性中，灵活性差
    public class RightAnimal
    {
        protected readonly string _name;

        public RightAnimal(string name) => _name = name;

        public void Eat(string something)
            => WriteLine($"- {_name} is eating a/some {something}.");

        public virtual void Run(int speed)
            => WriteLine($"- {_name} is running at {speed}km/h.");
    }

    public class RightSwan : RightAnimal
    {
        public RightSwan(string name) : base(name) { }

        // 忽略或报错
        public override void Run(int speed)
            => WriteLine($"- {_name} Ingore wrong skill.");
    }
}

更佳的处理

using static System.Console;

namespace CleanInheritance
{
    // 分配特有方法到子类，净化基类
    // 提升专有方法到技能类，并在构造器中传入，可完成更多孙类
    // 代码量大，安全性高，灵活性高
    public class BetterAnimal
    {
        protected readonly string _name;

        public BetterAnimal(string name) => _name = name;

        public void Eat(string something)
            => WriteLine($"- {_name} is eating a/some {something}.");
    }

    public class Beast : BetterAnimal
    {
        public Beast(string name) : base(name) { }

        public void Run(int speed)
            => WriteLine($"- {_name} is running at {speed}km/h.");
    }

    public class Bird : BetterAnimal
    {
        public Bird(string name) : base(name) { }

        public void Fly(int speed)
            => WriteLine($"- {_name} is flying at {speed}km/h.");
    }

    public class MoreBeast : BetterAnimal
    {
        readonly BeastSkill _skill;

        public MoreBeast(string name, BeastSkill skill) : base(name)
            => _skill = skill;

        public void Run(int speed) => _skill.Run(speed);
    }

    public class MoreBird : BetterAnimal
    {
        readonly BirdSkill _skill;

        public MoreBird(string name, BirdSkill skill) : base(name)
            => _skill = skill;

        public void Fly(int speed) => _skill.Fly(speed);
    }

    public class BeastSkill
    {
        readonly string _name;

        public BeastSkill(string name) => _name = name;

        public void Run(int speed)
            => WriteLine($"- {_name} is running at {speed}km/h.");
    }

    public class BirdSkill
    {
        readonly string _name;

        public BirdSkill(string name) => _name = name;

        public void Fly(int speed)
            => WriteLine($"- {_name} is flying at {speed}km/h.");
    }
}