Liskov Substitution Principle    裡式替換原則

• Liskov Substitution: 里氏替換。在任何基類類出現的地方，子類能直接替代基類，也就是說，基類有任何修改，都不會對子類功能產生影響。

• 以下例子：正方形是矩形嗎？

• class Rectange
              {
                  //public  int width { get; set; }
                 // public  int height { get; set; }
                  public virtual int width { get
   
  ; set; }
                  public virtual int height { get; set; }
                  public Rectange()
                  {
                  }
                  public Rectange(int width, int height)
                  {
                      this.width = width;
                      this.height = height;
                  }
                  
   
  public override string ToString()
                  {
                      return $"{nameof(width)}:{width} .{nameof(height)}:{height}";
                  }
              }
              class Square:Rectange
              {
  
                 // public new int width {  set { base.width = base.height = value; } }
                 
   
  // public new int height { set { base.height = base.width = value; } } 
                  public override int width {
                      set { base.width = base.height = value; }
                  }
                  public override int height {
                      set { base.height = base.width = value; }
                  } 
              }
  
              internal class Program
              { 
                  static public int Area(Rectange r) => r.width * r.height;
                  static void Main(string[] args)
                  { 
                      Rectange rc = new Rectange(2,3);
                      Console.WriteLine($"{rc} has a area {Area(rc)}");
                      Rectange square = new Square();
                      square.width = 4;
                      Console.WriteLine($"{square} has a area {Area(square)}");
  
                  }
              }