Prototype

Frequency of use:

Medium

UML class diagram

Participants

The classes and objects participating in this pattern are:

• Prototype  (ColorPrototype)
  • declares an interface for cloning itself
• ConcretePrototype  (Color)
  • implements an operation for cloning itself
• Client  (ColorManager)
  • creates a new object by asking a prototype to clone itself

Structural code in C#

This structural code demonstrates the Prototype pattern in which new objects are created by copying pre-existing objects (prototypes) of the same class.

     

using System;
 
namespace DoFactory.GangOfFour.Prototype.Structural
{
  /// <summary>
  /// MainApp startup class for Structural
  /// Prototype Design Pattern.
  /// </summary>
  class MainApp
  {
    /// <summary>
    /// Entry point into console application.
    /// </summary>
    static void Main()
    {
      // Create two instances and clone each
 
      ConcretePrototype1 p1 = new ConcretePrototype1("I");
      ConcretePrototype1 c1 = (ConcretePrototype1)p1.Clone();
      Console.WriteLine("Cloned: {0}", c1.Id);
 
      ConcretePrototype2 p2 = new ConcretePrototype2("II");
      ConcretePrototype2 c2 = (ConcretePrototype2)p2.Clone();
      Console.WriteLine("Cloned: {0}", c2.Id);
 
      // Wait for user
      Console.ReadKey();
    }
  }
 
  /// <summary>
  /// The 'Prototype' abstract class
  /// </summary>
  abstract class Prototype
  {
    private string _id;
 
    // Constructor
    public Prototype(string id)
    {
      this._id = id;
    }
 
    // Gets id
    public string Id
    {
      get { return _id; }
    }
 
    public abstract Prototype Clone();
  }
 
  /// <summary>
  /// A 'ConcretePrototype' class 
  /// </summary>
  class ConcretePrototype1 : Prototype
  {
    // Constructor
    public ConcretePrototype1(string id)
      : base(id)
    {
    }
 
    // Returns a shallow copy
    public override Prototype Clone()
    {
      return (Prototype)this.MemberwiseClone();
    }
  }
 
  /// <summary>
  /// A 'ConcretePrototype' class 
  /// </summary>
  class ConcretePrototype2 : Prototype
  {
    // Constructor
    public ConcretePrototype2(string id)
      : base(id)
    {
    }
 
    // Returns a shallow copy
    public override Prototype Clone()
    {
      return (Prototype)this.MemberwiseClone();
    }
  }
}

        
    

Output

Real-world code in C#

This real-world code demonstrates the Prototype pattern in which new Color objects are created by copying pre-existing, user-defined Colors of the same type.

    

using System;
using System.Collections.Generic;
 
namespace DoFactory.GangOfFour.Prototype.RealWorld
{
  /// <summary>
  /// MainApp startup class for Real-World 
  /// Prototype Design Pattern.
  /// </summary>
  class MainApp
  {
    /// <summary>
    /// Entry point into console application.
    /// </summary>
    static void Main()
    {
      ColorManager colormanager = new ColorManager();
 
      // Initialize with standard colors
      colormanager["red"] = new Color(255, 0, 0);
      colormanager["green"] = new Color(0, 255, 0);
      colormanager["blue"] = new Color(0, 0, 255);
 
      // User adds personalized colors
      colormanager["angry"] = new Color(255, 54, 0);
      colormanager["peace"] = new Color(128, 211, 128);
      colormanager["flame"] = new Color(211, 34, 20);
 
      // User clones selected colors
      Color color1 = colormanager["red"].Clone() as Color;
      Color color2 = colormanager["peace"].Clone() as Color;
      Color color3 = colormanager["flame"].Clone() as Color;
 
      // Wait for user
      Console.ReadKey();
    }
  }
 
  /// <summary>
  /// The 'Prototype' abstract class
  /// </summary>
  abstract class ColorPrototype
  {
    public abstract ColorPrototype Clone();
  }
 
  /// <summary>
  /// The 'ConcretePrototype' class
  /// </summary>
  class Color : ColorPrototype
  {
    private int _red;
    private int _green;
    private int _blue;
 
    // Constructor
    public Color(int red, int green, int blue)
    {
      this._red = red;
      this._green = green;
      this._blue = blue;
    }
 
    // Create a shallow copy
    public override ColorPrototype Clone()
    {
      Console.WriteLine(
        "Cloning color RGB: {0,3},{1,3},{2,3}",
        _red, _green, _blue);
 
      return this.MemberwiseClone() as ColorPrototype;
    }
  }
 
  /// <summary>
  /// Prototype manager
  /// </summary>
  class ColorManager
  {
    private Dictionary<string, ColorPrototype> _colors =
      new Dictionary<string, ColorPrototype>();
 
    // Indexer
    public ColorPrototype this[string key]
    {
      get { return _colors[key]; }
      set { _colors.Add(key, value); }
    }
  }
}

        

Output

.NET Optimized code in C#

The .NET optimized code demonstrates the same real-world situation as above but uses modern, built-in .NET features, such as, generics, reflection, LINQ, lambda functions, and more. You can find an example on our Singleton pattern page.

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