运算符重载，以及迭代器[foreach]示例

 以下代码来源于"c#高级编程(第4版)"，只不过我对它做了一些注释和修改

using System;
using System.Collections;
using System.Text;


namespace Wrox.ProCSharp.VectorAsCollection
{
    class MainEntryPoint
    {
        static void Main(string[] args)
        {
            Vector Vect1 = new Vector(1.0, 2.0, 5.0);

            Console.WriteLine(Vect1.ToString());
            Console.WriteLine(Vect1.ToString("IJK",null));
            Console.WriteLine(Vect1.ToString("VE", null));

            Vector Vect2 = new Vector(1.0, 2.0, 3.0);
            Console.WriteLine(Vect1 == Vect2);

            Double t = Vect1 * Vect2;
            Console.WriteLine(t);


            foreach (double p in Vect1)
            {
                Console.WriteLine(p);
            }
            Console.ReadLine();
        }
    }

    /**//// <summary>
    /// 声明一个矢量类(包含基本的x,y,z三个分量)
    /// </summary>
    struct Vector : IFormattable
    {
        public double x, y, z;       

        public Vector(double x, double y, double z)
        {
            this.x = x;
            this.y = y;
            this.z = z;
        }

        

        /**//// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="rhs"></param>
        public Vector(Vector rhs)
        {
            x = rhs.x;
            y = rhs.y;
            z = rhs.z;
        }

        /**//// <summary>
        /// 重载object类的ToString()方法
        /// </summary>
        /// <returns></returns>
        public override string ToString()
        {
            return "( " + x + " , " + y + " , " + z + " )";
        }


        /**//// <summary>
        /// 实现IFromattable接口，扩展自己的ToString()方法
        /// </summary>
        /// <param name="format"></param>
        /// <param name="formatProvider"></param>
        /// <returns></returns>
        public string ToString(string format, IFormatProvider formatProvider)
        {
            if (format == null)
                return ToString();
            string formatUpper = format.ToUpper();
            switch (formatUpper)
            {
                case "N":
                    return "|| " + Norm().ToString() + " ||";
                case "VE":
                    return String.Format("( {0:E}, {1:E}, {2:E} )", x, y, z);
                case "IJK":
                    StringBuilder sb = new StringBuilder(x.ToString(), 30);
                    sb.Append(" i + ");
                    sb.Append(y.ToString());
                    sb.Append(" j + ");
                    sb.Append(z.ToString());
                    sb.Append(" k");
                    return sb.ToString();
                default:
                    return ToString();
            }
        }

        /**//// <summary>
        /// 索引器
        /// </summary>
        /// <param name="i"></param>
        /// <returns></returns>
        public double this[uint i]
        {
            get
            {
                switch (i)
                {
                    case 0:
                        return x;
                    case 1:
                        return y;
                    case 2:
                        return z;
                    default:
                        throw new IndexOutOfRangeException(
                           "Attempt to retrieve Vector element" + i);
                }
            }
            set
            {
                switch (i)
                {
                    case 0:
                        x = value;
                        break;
                    case 1:
                        y = value;
                        break;
                    case 2:
                        z = value;
                        break;
                    default:
                        throw new IndexOutOfRangeException(
                           "Attempt to set Vector element" + i);
                }
            }
        }

        /**//*  
         * 考虑到精度问题，暂不用下面的写法来实现==运算符的重载
         * public static bool operator == (Vector lhs, Vector rhs)
                 {
                    if (lhs.x == rhs.x && lhs.y == rhs.y && lhs.z == rhs.z)
                       return true;
                    else
                       return false;
                 }*/

        private const double Epsilon = 0.0000001;
        

        /**//// <summary>
        /// 重载==运算符
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static bool operator ==(Vector lhs, Vector rhs)
        {
            if (System.Math.Abs(lhs.x - rhs.x) < Epsilon &&
               System.Math.Abs(lhs.y - rhs.y) < Epsilon &&
               System.Math.Abs(lhs.z - rhs.z) < Epsilon)
                return true;
            else
                return false;
        }

        /**//// <summary>
        /// 重载!=运算符
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static bool operator !=(Vector lhs, Vector rhs)
        {
            return !(lhs == rhs);
        }


        /**//// <summary>
        /// 重载+运算符
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static Vector operator +(Vector lhs, Vector rhs)
        {
            Vector Result = new Vector(lhs);
            Result.x += rhs.x;
            Result.y += rhs.y;
            Result.z += rhs.z;
            return Result;
        }

        /**//// <summary>
        /// 重载*运算符
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static Vector operator *(double lhs, Vector rhs)
        {
            return new Vector(lhs * rhs.x, lhs * rhs.y, lhs * rhs.z);
        }

        /**//// <summary>
        /// 重载*运算符
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static Vector operator *(Vector lhs, double rhs)
        {
            return rhs * lhs;
        }

        /**//// <summary>
        /// 重载*运算符
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static double operator *(Vector lhs, Vector rhs)
        {
            return lhs.x * rhs.x + lhs.y + rhs.y + lhs.z * rhs.z;
        }

        /**//// <summary>
        /// 重载GetHashCode(不重载的话，也可编译通过，但编译时会有一个警告)
        /// </summary>
        /// <returns></returns>
        public override int GetHashCode()
        {
                return base.GetHashCode();
        }

        /**//// <summary>
        /// 重载Equals(不重载的话，也可编译通过，但编译时会有一个警告)
        /// </summary>
        /// <param name="obj"></param>
        /// <returns></returns>
        public override bool Equals(object obj)
        {
                return base.Equals(obj);
        }

        /**//// <summary>
        /// 返回x,y,z的平方和
        /// </summary>
        /// <returns></returns>
        public double Norm()
        {
            return x * x + y * y + z * z;
        }

        enumerator class#region enumerator class
        
        public IEnumerator GetEnumerator()
        {
            return new VectorEnumerator(this);
        }

       
        private class VectorEnumerator : IEnumerator //要使用佚代器，必须实现IEnumerator接口
        {
            Vector theVector;      // Vector object that this enumerato refers to 
            int location;   // which element of theVector the enumerator is currently referring to 

            public VectorEnumerator(Vector theVector)
            {
                this.theVector = theVector;
                location = -1;
            }

            public bool MoveNext()
            {
                ++location;
                return (location > 2) ? false : true;
            }

            public object Current
            {
                get
                {
                    if (location < 0 || location > 2)
                        throw new InvalidOperationException(
                           "The enumerator is either before the first element or " +
                           "after the last element of the Vector");
                    return theVector[(uint)location];
                }
            }

            public void Reset()
            {
                location = -1;
            }
        }
        #endregion
    }
}

运行结果:
( 1 , 2 , 5 )
1 i + 2 j + 5 k
( 1.000000E+000, 2.000000E+000, 5.000000E+000 )
False
20
1
2
5