如何使用构造函数链接：base（）存在？

Question

Square上的构造函数需要设置自己的参数，并且参数继承自父类Polygon。

class Polygon
{
    public int NumSides;

    public Polygon(int numSides)
    {
        NumSides = numSides;
    }
}

class Square : Polygon 
{

    public int SideLength; 

    public Square (int sideLength) : this(numSides) : base(numSides)
    {
        SideLength = sidelength; 
        NumSides = NumSides; 
    }
}

Answer 1

public Square (int sideLength) 
        //: this(numSides)   // would call this ctor again, an endless loop
          : base(4)          // because a square has 4 sides
{
    SideLength = sidelength; 
    // NumSides = NumSides;  // action already taken in the base class
}

Answer 2

要传递给基类的参数必须是子类的ctor的一部分：

class Square : Polygon {

    public int SideLength; 

    public Square (int sideLength, int numSides) : base(numSides) {
        SideLength = sidelength; 
        // NumSides will be handled by base class ctor
    }

    // ctor overload with fixed number of sides for squares
    public Square (int sideLength) : this(sideLength, 4) {
    }
}