C# IFormattable 接口重写

 public class Racer : IComparable<Racer>, IFormattable
  {
    public int Id { get; private set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Country { get; set; }
    public int Wins { get; set; }

    public Racer(int id, string firstName, string lastName, string country = null, int wins = 0)
    {
      this.Id = id;
      this.FirstName = firstName;
      this.LastName = lastName;
      this.Country = country;
      this.Wins = wins;
    }

    public override string ToString()
    {
      return String.Format("{0} {1}", FirstName, LastName);
    }

    public string ToString(string format, IFormatProvider formatProvider)
    {
      if (format == null) format = "N";
      switch (format.ToUpper())
      {
        case "N": // name
          return ToString();
        case "F": // first name
          return FirstName;
        case "L": // last name
          return LastName;
        case "W": // Wins
          return String.Format("{0}, Wins: {1}", ToString(), Wins);
        case "C": // Country
          return String.Format("{0}, Country: {1}", ToString(), Country);
        case "A": // All
          return String.Format("{0}, {1} Wins: {2}", ToString(), Country, Wins);
        default:
          throw new FormatException(String.Format(formatProvider,
                "Format {0} is not supported", format));
      }
    }

    public string ToString(string format)
    {
      return ToString(format, null);
    }

    public int CompareTo(Racer other)
    {
      int compare = this.LastName.CompareTo(other.LastName);
      if (compare == 0)
        return this.FirstName.CompareTo(other.FirstName);
      return compare;
    }
  }