using System;

 using System.Collections.Generic;

 using System.Linq;

 using System.Text;

 using System.Threading.Tasks;

 namespace CSharp6Research

 {

     //分数

     public class Fraction

     {

         public int A { get; set; }

         public int B { get; set; } = ;

         public string Separator { get; } = "/";

         public string SeparatorSpaces { get; } = string.Empty;

         public double Value => (double)A / B;

         public int this[int index] => index ==  ? A : B;

         public int this[string index] => index == "A" ? A : B;

         public override string ToString() => $"{A}{SeparatorSpaces}{Separator}{SeparatorSpaces}{B}";

         public void Print() => Console.WriteLine(ToString());

         public Fraction()

         {

         }

         public Fraction(int a, int b)

         {

             A = a;

             B = b;

         }

         public Fraction(int a, int b, string separatorSpaces) : this(a, b)

         {

             SeparatorSpaces = separatorSpaces;

             if (string.IsNullOrEmpty(separatorSpaces))

             {

                 throw new ArgumentNullException(nameof(separatorSpaces));

             }

         }

         public static readonly Dictionary<string, Fraction> CommonFractions =

             new Dictionary<string, Fraction>

             {

                 ["zero"] = new Fraction(),

                 ["one"] = new Fraction(, ),

                 ["half"] = new Fraction(, ),

                 ["quarter"] = new Fraction(, ),

                 ["infinity"] = new Fraction(, ),

             };

     }

     public struct FractionStruct

     {

         public int A { get; }

         public int B { get; }

         public FractionStruct(int a, int b) { A = a; B = b; }

         public override string ToString() => $"{A}/{B}";

     }

     class Program

     {

         static void Main(string[] args)

         {

             foreach (var f in Fraction.CommonFractions)

             {

                 Console.WriteLine($"{f.Key} : {f.Value.Value}");

             }

             var fraction = new Fraction(, , " ");

             fraction.Print();

             try

             {

                 fraction = new Fraction(, , null);

             }

             catch (ArgumentNullException e) when (e.ParamName == "separatorSpaces")

             {

                 Console.WriteLine("separatorSpaces can not be null");

             }

             Fraction v;

             Fraction.CommonFractions.TryGetValue("harf", out v);

             v?.Print();

             var a = v?.A;

             Console.WriteLine(a == null);

             var b = v?["B"];

             Console.WriteLine(b == null);

             Console.WriteLine(v?.ToString() == null);

             Console.WriteLine(new FractionStruct(, ).ToString());

             Console.WriteLine(default(FractionStruct).ToString());

         }

     }

 }