Mixin in C#

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Mixin can be implemented in C# 3.0 using an extension method. 
Functionality can be added by extending 
the interface implemented by the class.
 
Consider the following example.

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   1:  using System;

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2:

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   3:  namespace Mixin

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4:

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   5:  {

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6:

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   7:  class Person : IPerson

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8:

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   9:  {

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10:

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  11:  private int _age;

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12:

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  13:  private string _name;

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14:

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  15:  #region IPerson Members

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16:

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  17:  public int age

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18:

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  19:  {

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20:

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  21:  get

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22:

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  23:  {

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24:

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  25:  return _age;

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26:

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  27:  }

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28:

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  29:  set

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30:

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  31:  {

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32:

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  33:  if (value > 0)

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34:

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  35:  {

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36:

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  37:  _age = value;

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38:

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  39:  }

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40:

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41:

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  42:  }

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43:

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  44:  }

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45:

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46:

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  47:  public string name

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48:

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  49:  {

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50:

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  51:  get

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52:

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  53:  {

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54:

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  55:  return _name;

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56:

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  57:  }

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58:

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  59:  set

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60:

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  61:  {

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62:

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  63:  if (!string.IsNullOrEmpty(value))

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64:

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  65:  {

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66:

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  67:  _name = value;

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68:

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  69:  }

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70:

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  71:  else

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72:

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  73:  {

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74:

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  75:  _name = "Unknown";

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76:

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  77:  }

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78:

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  79:  }

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80:

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  81:  }

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82:

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  83:  #endregion

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84:

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  85:  }

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86:

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  87:  interface IPerson

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88:

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  89:  {

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90:

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  91:  int age { get; set; }

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92:

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  93:  String name { get; set; }

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94:

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  95:  }

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96:

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  97:  static class ExtendIPerson

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98:

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  99:  {

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 100:

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 101:  public static bool CanDrive(this IPerson testPerson, bool isDriver)

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 102:

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 103:  {

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 104:

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 105:  if (isDriver)

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 106:

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 107:  return true;

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 108:

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 109:  return false;

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 110:

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 111:  }

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 112:

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 113:  }

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 114:

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 115:  class Program

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 116:

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 117:  {

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 118:

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 119:  static void Main(string[] args)

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 120:

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 121:  {

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 122:

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 123:  IPerson ip = new Person();

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 124:

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 125:

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 126:  ip.name = "ABC";

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 127:

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 128:  ip.age = 21;

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 129:

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 130:  if(ip.CanDrive(true))

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 131:

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 132:  {

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 133:

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 134:  Console.WriteLine(ip.name +" can drive");

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 135:

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 136:  }

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 137:

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 138:  Console.ReadLine();

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 139:

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 140:  }

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 141:

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 142:  }

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 143:

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 144:  }

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 145:

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In this example, we implemented mixin by extending the IPerson interface

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[line 87] using CanDrive extension method defined

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in the ExtendIPerson static class[line 101].

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Notice the code on line 130 ip.CanDrive - an example of C# mixin.

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Another explanation of the mixin can be found at

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http://mikehadlow.blogspot.com/2008/05/interface-extension-methods-mixin.html